How to recognize and treat skin reactions to processionary caterpillars

What skin reactions are caused by processionary caterpillars?

Contact with processionary caterpillar hairs causes the sudden eruption of small, raised, reddened papules that are very itchy and are usually distributed asymmetrically.

Where do skin reactions from processionary caterpillars appear?

Such reactions usually appear on the trunk and neck, but the limbs or face may also be affected.

Severe skin reactions to processionary caterpillars

The most severe form of skin reaction occurs when a processionary caterpillar falls from a tree and becomes trapped under clothing. In such cases, widespread itchy, stinging papules will form, accompanied by unbearable itching.

How to identify a skin reaction caused by processionary caterpillars

Skin reactions caused by processionary caterpillars present suddenly and cause the eruption of erythematous, itchy papules that are usually scattered across the upper trunk and neck in otherwise healthy individuals.
Direct skin contact with the caterpillar is not actually required to trigger a skin reaction.
This is due to the fact that the stinging hairs of the caterpillars are suspended in the air within their habitat, before falling onto humans, animals or the ground. Simply being in areas with trees infested by processionary caterpillars is enough to get a skin reaction from them.

When are skin reactions caused by processionary caterpillars most likely to occur?

Skin reactions caused by processionary caterpillars occur from May to July, that is, when the caterpillars are active and coming out of the nests.

What causes skin reactions from processionary caterpillars?

Reactions are caused by the penetration of the tiny hairs that line the body of the caterpillar into the skin.

About processionary caterpillars

What are processionary caterpillars?

The processionary caterpillar (Thaumetopoea pityocampa) is an insect of the Lepidoptera order, belonging to the Notodontidae family.

Why are they called processionary caterpillars?

These Lepidoptera are popularly called “processionary” caterpillars because they descend to the ground in a single-lined ‘procession’ down the tree trunk.

Where do they live?

Processionary caterpillars are widespread throughout the Mediterranean basin and are be commonly found in pines, as well as oaks, larches, cedars and many other trees. The caterpillars cause dangerous defoliation to trees by feeding on leaves.
Their nests are white, triangular and silky-looking, and are usually clearly visible hanging from the ends of branches.

How to prevent skin reactions from processionary caterpillars

Skin reactions to processionary caterpillars are difficult to prevent. Any areas where there are trees with caterpillar nests should be identified and avoided where possible. If walking in wooded areas, wear tight-fitting, opaque clothing to prevent stinging hairs from penetrating the skin.

Treating skin reactions to processionary caterpillars

By the time the itchy rash has developed, skin damage will have already occurred and, therefore, it’s important to act quickly on symptoms. Oral antihistamines can be administered to reduce itching, although in dermatological practice, they have little effect.
More effective is the application of Astringent Gel, which has anti-itching, astringent and antiseptic properties that help to prevent skin infections that may occur from scratching. Astringent Gel can be applied several times a day as needed.
The skin reaction to processionary caterpillars will wear off in about a week, but it is important to avoid direct sunlight during this time.

To avoid

Antihistamine or anti-inflammatory creams must be avoided. In addition to not being effective on skin reactions caused by processionary caterpillars, both are photosensitizing and further increase the skin’s vulnerability to direct sunlight at a time of the year when the sun is at its strongest.
Cortisone creams should also be avoided because they do not treat the papules that form where the stinging hair has penetrated.
They can also worsen inflammation, make the reaction last longer and can increase the risk of infection from scratching.
Finally, vigorously and/or regularly washing the affected area in an attempt to get rid of the irritating hairs often only worsens itching.

FAQs on skin reactions from processionary caterpillars

Are hairs from the processionary caterpillar toxic?

It is not known whether the hairs of processionary caterpillars contain any particular toxic proteins. What is known, however, is that the hairs are shaped like serrated spines, meaning that when they penetrate the skin (usually into a hair follicle) they cause severe irritation and the release of histamine, as the body’s attempt to mediate itching.

Can contact with the hairs of the processionary caterpillar be toxic?

Usually contact with the hairs of the processionary caterpillar is not dangerous, but cases of anaphylactic shock have been reported in particularly sensitive individuals. If the hairs come into contact with the eyes, they will cause acute conjunctivitis with considerable watering and redness. If inhaled, they can cause coughing and difficulty breathing. If ingested, the tongue may swell and the stomach will likely hurt.

Are processionary caterpillars also dangerous for animals?

Processionary caterpillar hairs are a particular risk to dogs, horses and woodland animals who come into contact with them from sniffing the ground and eating grass. Damage will appear to the nose area, on the tongue or in the mouth, but if ingested, the hairs can prove fatal to the animal.

Why are some individuals confused about skin reactions caused by processionary caterpillars?

The actual source of skin reactions caused by processionary caterpillars can sometimes cause confusion, as the rash usually appears hours, or even days, after contact with the stinging hairs. This means that the patient is usually unable to link the skin reaction to having been in woodland or under trees.

Conclusion

Instead of giving up on going outside and enjoying nature, it’s best to learn about recognizing skin reactions caused by processionary caterpillars, and being prepared in how to treat them properly.