Insect repellents (usually also effective for arachnids) are available in various forms, including lotions and aerosols that can be applied to the skin, and others that can be applied to clothing. There are also devices that generate repelling scent, such as some mosquito coils and citronella candles. Some of the repellents are toxic also for humans or pets, check warnings.

Also clothes and equipment can be treated with repellents or insecticides; some are suitable for this use. Mosquito nets are commonly treated at the factory.

• DEET (diethyl toluamide) – effective at concentrations of 10% and up; its strength plateaus at around 50%, and the efficacy–safety balance is probably best at 30%. DEET-based repellents are generally the most common, the most effective overall along with icaridin, and are readily available from pharmacies, supermarkets, and vendors at larger airports. DEET should not have harmful effects when applied to the skin as instructed, but don't inhale it (or drink it). If you need repellents for an extended time, recommendations for minimizing absorption may be relevant. Some people are sensitive to DEET. Sunscreen increases DEET penetration and may intensify its side effects. DEET also dissolves plastic and can damage plastic parts of electronics, outdoor gear and clothes. Some people also find its odor unpleasant.
• Icaridin, also known as picaridin – formulations with 20% icaridin are as effective as the more common DEET, with no side effects, no odor and no damage to plastic parts and synthetic fabrics. Icaridin repellents are more expensive than DEET repellents and are available in limited areas as they are newer. Icaridin spray repellents can usually also be applied to clothing, lasting as long as on the skin.
• Oil of lemon eucalyptus (p-menthane 3,8-diol) – another option for those sensitive to DEET. Considered to be the strongest of the plant-based repellents and according to some studies may be similar to DEET in terms of effectiveness, although it wears off faster. Has a strong lemon-like odor, but without the acrid chemical edge typical of DEET.
• Various other herbal or plant-based repellents are also available, but their effectiveness is extremely limited.

Although the repellents and insecticides should be safe for humans when used according to instructions, you should be cautious. Wash your hands after handling them, to avoid getting them in your eyes or mouth, avoid applying them too near eyes and mouth, apply moderately on ears and don't treat socks and underwear. Children should not handle repellents, an adult should do it, avoiding applying it to their hands. In contrast to sunscreen, repellent should be applied only thinly.

Like sunscreen, insect repellent will become ineffective if not reapplied every few hours, more often if you are swimming, sweating or getting rained on, and for some of the products.

Mosquito coils, usually permethrin-based (thus pesticide rather than repellent), provide effective protection for up to 8 hours in spaces up to 30 cubic meters (a small room). They usually come with little stands: bend the center part upwards, slot the middle of the coil on the pointy bit, heat the other end with a flame until it catches fire, then blow it out and let the end smoulder. The main danger with these is the risk of fire: place the coil on a ceramic plate or other fireproof platform and extinguish it before going out or going to sleep. The smell will usually fade pretty fast from your clothes and other belongings. For indoor use, there are also plug-in electrical devices that dispense an insecticide and/or a repellent into the air.

Permethrin- and pyrethroid-based mosquito coils and repellents are fatal to cats, so those who travel with such pets should consider other mosquito repellents.

There are also electric devices ("bug zappers") that attract insects and kill them. These may reduce the annoyance level on a balcony or patio, but not usually to zero. Most use light to attract the insects; this does not work for mosquitoes.

The common black ants are a problem mainly because they get into food. However, there are types of ants that can make for an uncomfortable or even dangerous encounter. The three types of stinging ants are:

• Bull ants — around 90 Australian species of ant, endemic to Queensland, New South Wales and New Caledonia, identified by their slender bodies 15–40 mm long, large eyes, and long mandibles
• Fire ants — 285 species worldwide, typically with black-reddish bodies, 2–6 mm (0.079–0.236 in) in length
• Ponerine ants — 1,600 species worldwide, which can be identified by a very constricted "waist" and large body size

Ant stings can really hurt, and accidentally walking on a fire ant nest can give a person – especially a toddler – an experience they won't soon forget. Worse yet: don't put your underwear on a nest when changing to swimwear. Though painful, bites will usually clear up within a couple of days if left alone. For cases where there are multiple bites, hydrocortizone or aloe vera is sometimes applied topically, or antihistamines may be taken orally. A few unfortunate people are allergic, and for such people stings may lead to anaphylactic shock, which can be lethal.

These tiny nuisances tend to nest under beds or in other furniture, coming out at night to feed on the blood of human victims who typically do not feel bites at the time. Infestation can be found almost anywhere in the world, not necessarily only in low cost accommodations, they are becoming an increasingly common problem due to more international travel and insecticide resistance.

Bites may be hardly noticeable at first, but can sometimes provoke rashes, allergic reactions, or other skin irritations. Some people do not develop response to bites at all so may not even be aware they have been bitten. If you are travelling cheap and happen to detect a faint odor of rotten raspberries in your hotel room, or if you find small, mysterious red bites, especially three bites in a line, on your skin in the morning, you might consider changing your choice of accommodations. When necessary, take extra precautions such as checking crevices / edges of mattresses for signs of black dots (bedbug feces) or bug carcasses. Bedbugs can harbor in a variety of places, including mattress seams, cracks in the wall, luggage, inside of vehicles, within furniture, among bedside clutter—even inside electrical sockets and nearby laptop computers.

You do not want to take these home with you. When visiting a new lodging, it is advised to check the bed before taking suitcases into the sleeping area and putting the suitcase on a raised stand or in the tub to make bedbugs less able to crawl in. Clothes should be hung up or left in the suitcase, and never left on the floor. As many as 5% of hotel rooms may be infested. One extermination company advises travelers not to sit down on public transport; check office chairs, plane seats and hotel mattresses, and monitor and vacuum home beds once a month. Avoid unpacking into places where the bugs may be dwelling and wash your spare clothes before the bugs have a chance to hide away. After visiting an infected site, take precautions: for instance, check your shoes when you leave, change clothes in a garage before returning to your home, and put the used clothes in a clothes dryer outside the house.

Permethrin-treated fabrics kill bedbugs. Treating items like the outside of your sleeping bag can partially protect you from bites, and treating your backpack can prevent them getting into spare clothes.

Once bedbugs have made it to your house, they're hard to get rid of, partly because they can survive up to a year without feeding. Treatments include heating the room to 50 °C (122 °F) for more than 90 minutes, frequent vacuuming, washing clothing at high temperatures, and pesticides.

People who are allergic to stings need to exercise great caution, because one sting can be fatal for them. Consult your doctor about carrying an epi pen for emergency first aid (which needs quick follow-up care) and other precautions. For anyone else, stings can be very painful, but unless you are stung near the trachea (e.g. if you get one into your mouth) or are stung by an entire hive, there is usually very little risk of serious complications. However, varieties such as the 'Asian Giant Hornet' (found in Japan, Korea and China) can deliver stings that are life-threatening even to people without an allergy.

Honey bees may swarm out and defend their hive against perceived threats, but single individuals will usually try to just mind their own business, as a sting will end their lives.

Hornets and wasps sting more readily than bees because stinging is a simpler act, and they can sting multiple times. The ones you're most likely to encounter in many parts of the world are a group of black-and-yellow wasp species colloquially known as yellowjackets. They probably won't sting you for no reason, but if you are eating or drinking outside and a swarm of yellowjackets decides they want what you're having, you're best off letting them have it.

Hoverflies pretend to be yellowjackets but are completely harmless. They tend to be smaller and are easily identified by their flight behavior, as they often hover in one spot for a couple of seconds. You might encounter them in settings with lots of flowers around, as they feed on pollen and nectar.

The caterpillars of the South American giant silkworm moths (Lonomia) are highly toxic – to the point that getting stung by a couple of them while casually leaning against the wrong tree can get you killed.

The hairs of some other moths and caterpillars can cause allergic reactions and a contact dermatitis called lepidopterism. The oak processionary (Thaumetopoea processionea) common in parts of Europe is one of them, and its range is expanding due to climate change. They are difficult to get rid of, and control efforts are often focused on places like parks and residential areas, where there are many people around. Nests in the forests and elsewhere in the countryside may go unnoticed or untreated, so when traveling to risk areas in late spring and early summer, it is a good idea to stay away from furry-looking oak trees. After accidental contact, change your clothes as soon as possible, wash your skin and hair, and see a doctor if you notice any skin irritations.

Centipedes have long bodies with many segments, many legs, and a pair of antennae. They can bite, but only the larger ones can actually penetrate human skin. Their venom can be dangerous to children and induce an anaphylactic shock in people that are allergic to bee stings. For everyone else, bites of large centipedes may be painful but are usually harmless.

The similar-looking millipedes are all harmless to humans. They have two pairs of legs on the underside of most segments, while centipedes have one pair attached to the sides of most segments.

Chiggers, also known as harvest mites or berry bugs, are nearly-microscopic mites whose larvae bite people and animals and cause intense itching. They act similarly to ticks, inhabiting tall grass and unkempt forest, waiting to attach to a suitable host. Luckily, they don't spread disease nearly as well as ticks, and they fall off of the skin very easily, so they are more of a nuisance than anything. Wear long pants and sleeves and avoid tall grass to steer clear of chiggers.

Cockroaches are common carriers of disease and you surely do not want to handle them or allow them to get into your food. Quite a few people are allergic to cockroaches, and this allergy is a major cause of asthma in places with large roach infestations, like poor areas of American cities. In some parts of the world, such as Thailand, large roaches called waterbugs are considered a delicacy and are for sale in markets for human consumption.

It pays to check on what kind of flies are present where you are visiting. House flies can spread infection and are a common contaminator of food. In some countries exposed waste makes flies particularly dangerous by what they can spread.

Some types of flies bite but, unlike female mosquitoes, they have many sources of food other than blood, so they may leave you alone and be mostly just a nuisance. However, horseflies have a particularly annoying bite, and there are parts of the world where black flies are a horrible scourge. Even worse, certain types of flies are very dangerous, like the tsetse flies that spread sleeping sickness, which kills tens of thousands of people or more every year in East Africa. In Australia, non-biting flies can swarm and simply make it difficult to do anything without whisking them away from the face, leading to various nets and hat attachments as essential clothing.

Tiny biting flies (aka midges) are not unknown in remoter parts of the Scottish Highlands, Northern Europe, Scandinavia and Russia.

Mite is a bit of a catch-all term for a wide range of 8-legged critters, including Ticks and Chiggers.

The red mite Dermanyssus gallinae mostly feeds on birds and may infest humans, e.g. via feral pigeons and backyard poultry.

Most other mites are harmless to human health, but some are still a major pest in other ways. The Varroa mite, for example, is a big threats for honey bees.

See also: Infectious diseases#Mosquito-borne diseases

Mosquitoes exist around the world, especially in wetlands. In parts of the tropics, mosquitoes carry malaria, dengue fever, Zika virus, or yellow fever. Other diseases, including West Nile virus, can be spread by mosquitoes in some temperate latitudes. Swarms of mosquitoes can be a problem also where they do not carry diseases, and even a single mosquito bite can be an irritation and annoyance as it itches for days. Your body gets used to them over time, so bites itch much less for locals.

Prevention is better than cure: cover arms and legs as much as possible, and use repellents on exposed skin, especially during peak biting hours, from several hours before sunset to a few hours after sunrise. There are mosquito hats (or nets to draw over your hat, which pack compactly), to use where the problem is severe. Use insect screens or insect nets where you sleep.

There are claims that ultrasonic sound can repel mosquitoes, and there are devices on the market to do this. However, the claims seem to be completely bogus.

In areas where mosquitoes are a problem, typical precautions include:

• long sleeves and pants – loose fitting and light-colored
• wearing white or bright clothing – black clothing attracts mosquitoes
• avoid perfume and scented products since those may attract mosquitoes
• mosquito nets – can be placed over your bed, hammock, or sleeping bag
• mosquito hat – with a net from the hat brim to your shirt
• staying inside at dawn or dusk – daybreak and nightfall are higher activity times for many mosquitoes
• insect repellent – topical lotions or sprays for both skin and clothing

Sleep in rooms where you can close the windows and doors (air-conditioned if they would otherwise be too warm), or have insect screens over the windows, to prevent mosquitoes entering. Be sure to check the screens for defects before relying on them, and be quick at the door in the evening. Having a fan switched on can help for mosquitoes that still are in the room, as the moving air makes it difficult for mosquitoes to land. If the mosquitoes indoors are few, you might want to kill them by hand, but usually some leave their hideouts ten minutes after you got into bed and switched off the light – for the umpteenth time.

Most electronic bug zappers are not effective against mosquitoes since mosquitoes are not attracted to light. There are some models which emit carbon dioxide or octenol (found in the breath of mammals) so they do attract mosquitoes.

A major method of controlling mosquito population is to eliminate standing water where they breed. They do not need much; even a bit of water around the base of a flower pot is enough. In some countries there are substantial fines for anyone found to have standing water on their property; this is one reason that Singapore is now low-risk for both dengue and malaria.

When camping, it may be wise to avoid setting up near areas with stagnant or standing water. Higher ground with more wind may have less mosquitoes. When camping or sleeping indoors without screens in areas where mosquitoes are dangerous, use a mosquito net that has been treated with permethrin. As mosquitoes are very persistent insects that will keep trying to find a way to reach you, make sure the net is securely tucked under your bed or sleeping mat.

While spiders and their webs can be a nuisance, most spider species are not dangerous to humans. Big spiders such as the huntsman can give you a strong bite, but it is not venomous.

For the small number of venomous spiders that can potentially be deadly, such as the Sydney funnel web and the redback in Australia, fatalities are extremely rare. Bites are usually by accident, but if it happens then try to catch the spider (or take pictures) for identification, and seek medical assistance immediately.

In North America, black widows (black with a distinctive red hourglass shape on the back) and brown recluses are venomous. Their bites can be serious; death is uncommon but possible, so seek medical attention. These are shy spiders and are unlikely to bite people unless they feel threatened.

To avoid an accidental encounter with a spider, be careful where you stick your hands and bare feet. Shake out shoes and clothes that haven't been worn recently.

See also: Infectious diseases#Tick-borne diseases

Ticks (Ixodida) are small, eight-leg arachnids that prey on large animals, such as humans. They live on grass or bushes and hop onto any passing mammal. Young ticks, nymphs, are barely visible to the naked eye; when fed with blood, they can become as big as a pin head.

Ticks are among the most common visible parasites in temperate areas such as Europe and North America. However you may encounter ticks in the tropical regions as well, for instance in the Amazon rainforest. In Australia kangaroo ticks are very common and require checking for in areas frequented by kangaroos.

Ticks can be a nuisance in outdoor life, especially when hiking and travelling with pets, and in some parts of the world, certain kinds of ticks can carry some quite nasty diseases:

• Tick-borne meningoencephalitis (TBE) — found in temperate regions of Europe and Asia — is a serious disease which requires hospitalization and can be fatal. There is no specific treatment against TBE and it reduces to a symptomatic therapy. There is vaccination available, relevant if staying a longer time in the riskiest environments.
• Lyme disease (borreliosis) — found in much of the US and Europe — can often be noticed by a red ring forming on the skin, a week or so after the bite. However, not everyone shows that symptom. In the beginning, when symptoms are mild and temporary, it is easily treated with antibiotics. Untreated borreliosis can give serious symptoms later. Treatment at this stage is difficult and rehabilitation not guaranteed.
• Rocky Mountain Spotted Fever (RMSF) — which occurs through much of North and Central America and parts of South America — is a bacterial infection and responds well to treatment with antibiotics. Usually the first symptoms are a high fever and splitting headache, often followed a few days later by a rash that starts around the wrists and ankles. The disease is not very dangerous with proper treatment but can be fatal if not treated promptly.
• Crimean-Congo hemorrhagic fever (CCHF) — found in Africa, the Balkans, the Middle East, Russia and Ukraine, and with some cases as far east as India — is a severe infection in humans with a mortality rate up to 40% within a week if untreated. It requires immediate hospitalization — effective treatment against it exists but preventative vaccines are in an experimental stage.

The bites of certain ticks can also lead to a condition known as "alpha-gal allergy". When such a tick bites, it releases saliva in its victim that contains a sugar known as "alpha-gal". This sugar is present in all mammals except apes, Old World monkeys, and humans. The presence of this sugar in the human bloodstream provokes a strong immune reaction. When the victim consumes the meat of any other mammal, or in some cases even other mammalian products such as milk or gelatin, an allergic reaction will follow anywhere from 3 to 8 hours later. In some people, this allergy will subside over months or years if they're not bitten by another tick. Also, sufferers need not become strict vegetarians, as poultry and seafood do not contain alpha-gal and thus will not trigger the allergy.

If you have been exposed to ticks and become ill, see a doctor immediately. Similarly, if you've always been able to eat mammalian meat but have allergy symptoms, nausea, or diarrhea a few hours after eating such a meal, also see a doctor immediately.

How to remove a tick

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To reduce the risk of infection, you should remove the tick from your skin carefully, but without unnecessary delay (leaving it overnight will drastically increase the risk). Infection with borreliosis, which is the most common of the diseases, does usually not happen until the tick has been attached for hours, but TBE can be transmitted much quicker. Be patient and thorough when removing ticks to prevent the mouth parts from breaking off under the skin and to avoid squeezing the tick, as that would increase the risk of infection. The safest way to remove a tick is a dedicated tick removal tool from the pharmacy, which makes removal of even the smallest ticks relatively safe and easy. Fine-tipped tick tweezers are another option, but they are more difficult to use safely – especially with shaky hands or fading eyesight.

After removal, wash the bite with alcohol, iodine, or soap and water. Save the tick in a plastic bag, with a wet tissue if it's still alive, so that it can be tested if you develop symptoms. If you experience symptoms relating to the bite, you should go visit a doctor as soon as possible. Similarly, if you develop a rash or fever within weeks, seek prompt medical attention and remember to mention the tick.

If you see a scorpion, watch out. At best, their sting is very painful. At worst, in some parts of the world, a scorpion strike can be fatal. In general, scorpions are more interested in smaller creatures they can eat than they are in you, but they do need to be respected. If you are travelling in an area where scorpions are endemic, take special care not to leave your luggage open overnight, and check inside your shoes before putting them on, in case a scorpion has decided to make its home there.