Key information

People can be bitten by insects (which have six legs) such as mosquitoes, midges and horseflies and arachnids (which have eight legs) such as mites and ticks. In this module the term ‘insect’ is used to include both groups.

Some insects (such as mosquitos, bed bugs and fleas) have piercing mouthparts which cause little trauma and may not be noticed immediately. Other insects (such as horseflies and midges) lacerate the skin and lap up blood from the wound. Such bites are painful and are noticed immediately.

Stinging insects include bumble bees, honeybees, wasps and hornets. They inject venom which contains a mixture of pharmacologically active substances (e.g. allergens, histamine). The sting is usually felt immediately. Honeybees have a barbed stinger and venom sac; this is left in the skin as the insect flies away. The diagnosis of infected insect bites and stings is based on the history and examination.

The appearance of bites and stings varies. Many will start as a small red mark or papule. Sometimes there is inflammation or swelling around the initial bite or sting and this may develop over several days. Occasionally insect stings can cause large local reactions, with inflammation spreading over an area greater than 10cm within 24-48 hours and resolving in three to 10 days.

See images at: nhs.uk/conditions/insect-bites-and-stings and descriptions at: cks.nice.org.uk/topics/insect-bites-stings/diagnosis/assessment.