Hives caused by exposure to the Pine Processionary Caterpillar

Advice on action and prevention against caterpillar bites

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Sex and age of patient

Male 26 years of age, no previous illnesses related to this consultation or under any treatment apart from having taken Ebastine, thinking it was an allergic reaction.


The patient arrived with multiple insect bites, highly pruritic after 12 days of very slow remission.

He started to notice itching in both his torso and extremities after having been on a bike ride through an area of pine forest in Valencia. All of his friends taking part in the ride presented the same symptoms but nobody noticed anything having happened during the ride. After 8 days, the patient continued with intense itching and dysthymia, a dry mouth, drowsiness (he was taking Ebastine) and highly inflamed lesions on the skin, some which evolved into haematomas.

Physical Examination

FC: 63 lpm TA: 115/63 mmHg Tª 36,0º. Good general state. Organs and systems unchanged.

Skin: multiple lesions compatible with insect bite (up to 100) scattered across the torso and the extremities apart from the face and the palms of the hands and bottom of the feet, polymorphs’-some with underlying inflammatory erythematous, others very hard and others in the process of forming disc shaped bruises.

Blood analysis completely normal.


This is quite a straightforward case and its diagnosis is not difficult (perhaps, only in defining the insect responsible), but the result of this illness is very uncomfortable and nobody is immune to it.

The caterpillars, the adolescent form of moths and butterflies and in particular those of the processionary Caterpillar, are the larvae of the Nocturnal Lepidoptera Thaumetopoea pityocampa. It is a plague in the forests of Mediterranean countries and is extending to the forests of northern Europe as a result of global warming. In the region of Huesca during 2010 around 100 people suffered the consequences of coming into contact with this animal, which is why we think it is worthwhile to describe the nature and the symptoms of this illness and basic methods of treatment.

During the last three larval stages of the Caterpillar they grow prickly hairs, which they use as protection against predators. These hairs break loose easily and can be carried by the wind. Sometimes these fibres contain toxins, which are freed on contact with skin and can produce various pathologies, one of them being an effect on the skin that generally manifests as contact urticaria and papular dermatitis. They are also capable of attaching to, and irritating the conjunctival mucous membrane and penetrating the respiratory tract causing similar of symptoms. During the last few years there have been cases of anaphylactic reactions.

The pathogenic mechanisms implicated include mechanical or irritation and allergy due to hyper sensibility measured by IgE, where the reaction is immediate, repetitive and progressively worsens.

Being attacked by a Caterpillar or being bitten can be very painful, depending on the species. Luckily, this type of injury is not normally serious in the majority of people, but the pain and the stinging should be treated quickly and if you have an allergy problem it would be sensible to watch out for any reaction you might have.

Symptoms and treatment of Caterpillar stings

  1. Study the types of reactions when caused by a Caterpillar sting:
    • Dermatitis: stinging and contact dermatitis, boils, hives and small red bumps, pain.
    • Acute conjunctivitis, if the hairs have penetrated the eyes.
    • Lepidopterism: urticaria (an itchy rash or urticaria), inflammation of the upper respiratory tract, nausea, vomiting, headaches and bronchospasm.
    • Contact with the Asian Caterpillar (Dendrolimus pini), can initially cause dermatitis and can also lead to certain types of arthritis (polyarthritis, polychondritis or chronic osteoarthritis).
    • Bleeding and kidney failure can result from having contact with the South American Lonomia Caterpillar. Any contact with this Caterpillar can be dangerous, or even fatal if there are large concentrations of them (such as when collecting vegetation where there are allot of them). This Caterpillar only exists in Brazil and there is an antidote available.
  2. Reassure the victim. It is easier and much less stressful to treat a bite if you are calm. Also the venom tends to disperse faster if the patient moves around. Try to understand that the majority of bites or stings from caterpillars in North America and Europe, although very painful, are benign. Death from Caterpillar bites or stings is very rare.
  3. Remove the Caterpillar from the body. Use either forceps or tweezers but do not use bare hands.
  4. Place sellotape or something similar over the bite. Stick the tape down and pull it off repeatedly. This will the remove barbs, hairs and toxins. Do this using a new piece of tape each time so as not to introduce more hairs onto the skin.
  5. Clean the affected area with soap and water and wash any contaminated clothing in hot water.
  6. An ice pack will also help. Apply a cold compress over the affected area after having cleaned it. Once the stinging sensation has reduced (after 15 or 20 minutes), apply a mixture of bicarbonate of soda and water.
    • Apply a topical anaesthetic, if you have one available.
    • Painkillers such as paracetomol or Nolotil can help.
    • You can reduce the inflammation by elevating the affected area.
    • If necessary you can reapply the cold compress for 15 to 20 minutes every hour.
    • You can substitute a damp cloth for the cold compress.
  7. Keep an eye on the bite. Look for a discharge, rash, inflammation or discolouration; should you see no improvement in the symptoms, seek medical advice. (If the patient suffers from asthma, hay fever or other allergies or if allergic symptoms start to appear, go straight away to see a Doctor).
  8. Take note of the Caterpillar that caused the problem. This can be important later if other symptoms appear or if they get worse. If you don’t have a camera handy, then make a mental note of its features (colour, length, texture, how many there were and the type of hairs). The caterpillars you have to be careful of are:
    • The pus Caterpillar (Megalopyge opercularis): this is considered to be the most dangerous type of Caterpillar in the United States It is the larval form of the Flannel Moth and is found from Maryland to Florida. The larger Caterpillar is the most dangerous. It is usually found in various trees and shrubs, including, elm, maple, hackberry, oak, sycamore, etc. It is most common from June to September. All patients feel pain after being bitten by this Caterpillar but only one in three will suffer headaches, muscle spasms, breathing difficulty and seizures.
    • Stinging rose caterpillar (Pink chopper) is often found in in shrubs and the lower branches of cercis trees, oaks, pecan, bayberry, wild cherry and sycamore.
    • Saddleback Caterpillar: if stung by this Caterpillar is will cause severe irritation. It is often found in in the dead leaves of trees (chestnut, cherry, oak, linden and plum) and sometimes in maize.
    • Euclea delphinii caterpillar: this is usually found in oak trees, but also in chestnut, beech, willow, pear, bayberry, oxidendro, cherry amongst other trees.
    • Buck moth caterpillar (Hemileuca maia): this caterpillar has venomous spines and is found in oaks, beech in in general from spring through to the middle of summer.
    • Lo moth Caterpillar: this also has venomous spines. It is found in many plants, including, maize, roses, willow, linden, elm, oak, carob, Apple, beech, ash, currant and clover, usually from spring to the middle of summer.
    • Hag moth caterpillar, Phobetron pithecium: this Caterpillar resembles a dried leaf and is usually found in the lower branches of trees and shrubs, including, oak, chestnut, dogwood, sassafras and ash.
    • Spitfire Caterpillar (Australia): this Caterpillar can spit a liquid that causes contact dermatitis if the hairs break the skin.

Advice on dealing with and prevention of Caterpillar bites

  • It is possible to have an allergic reaction to Caterpillar bites and some of them have particularly potent venom. Look for symptoms such as swelling of the face, the throat, or tongue, discolouration of the mouth, breathing difficulty or a rash that spreads quickly. They may indicate a severe reaction that requires immediate medical attention.
  • Never let children or pets play with unknown creatures, even something as small as a Caterpillar. Teach children to avoid prickly or bright coloured caterpillars, these characteristics often nature’s warning that they are poisonous.
  • Even caterpillars that don’t sting can be dangerous in your garden. Look for nests covered in a white silk that may be in nearby trees. Some of the “Thyridopteryx ephemeraeformis” species or the Asian gypsy moth are parasites that can kill trees.
  • It appears that antihistamines are not helpful against caterpillar bites.
  • Thing’s you’ll need to treat bites:
    • Tape (Sellotape, Scotch Tape, Duct Tape) or a commercial face mask
    • A mixture of bicarbonate of soda and water
    • Cold compresses or a pack of frozen food (or anything very cold or frozen).
    • Clean water and soap
    • Painkillers

Road safety advice

  • A Caterpillar bite, as we have said, can cause itching and a rash. You must take care when driving with any of theses irritations as they can affect a driver’s concentration.
  • If you have taken painkillers or antihistamine, be aware of the side effects of these drugs, which can be drowsiness and slow reactions.


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