Distribution

More than 200 species with urticating hairs are distributed throughout the world from tropical to temperate zones.

1. North America, Europe, North and Central Asia
2. North, Central and South America
3. Central Asia, North Africa
4. North, Central and South America
5. North America, Europe, Africa, Madagascar, Asia, New Guinea, Australia
6. North and Central America
7. North, Central and South America
8. North and Central America, Europe, Central and East Asia
9. North America, North and Eastern Africa, Madagascar
10. North America
11. Central and South America
12. North America, Europe, North Africa, Asia, New Guinea, Australia
13. North America, Mexico, Europe, North Africa, Asia
14. Southern USA, Central and South America
15. Bolivia
16. North and Central America, Europe, North Africa, Asia
17. Australia
18. North America, Mexico, Europe, North Africa, Asia, New Guinea, Australia
19. Southern USA, Central and South America
20. Eastern and southern USA, Central and South America
21. Europe, North Africa, Middle East
22. Europe, North Africa, Western Asia

Biology

The order of butterflies and moths (Lepidoptera) includes around 165,000 known species. They pass through the following stages during their ontogenetic development: egg, various larval stages (caterpillar), pupa and adult. Venom-filled hairs may be present at all of these stages, but they are most common in caterpillars and adult animals. Some species place protective urticating hairs on their clutch of eggs.

  Fig. 4.87 Hylesia urticans. This species is known to cause envenoming in South America in the adult stage.

  Fig. 4.88 The larval stage of Automeris io causes erucism in eastern USA.

Basically there are two types of urticating hairs:

a. Sharp, hollow urticating hairs that detach easily (→ caterpillars and adult animals),

b. hollow, firmly attached hairs (spines or setae) that only break off upon contact (→ only caterpillars).

The hairs are either smooth or have barbs or sharp processes. The fluid in the hollow spaces may contain dolorogenic, vasoactive substances such as histamine and kallikreins.

In older classifications envenoming caused by caterpillars is termed "erucism" and that caused by butterflies and moths "lepidopterism".

Diaz (2005) provides a new classification according to the envenoming syndrome, regardless of whether it is caused by caterpillars or adult animals:

1. Erucism: local effects caused by contact with or airborne exposure to urticating hairs, spines or toxic haemolymph. For example, caterpillars of the moth species Automeris io (Io moth) or Sibine stimulea (saddleback) are associated with erucism.

2. Lepidopterism: systemic effects of a marked allergic/autopharmacological nature caused by direct or aerosol contact with urticating hairs, spines or body fluids of caterpillars, cocoons or moths. Some examples of caterpillars that can cause lepidopterism are Lymantria dispar (gypsy moth), Euproctis sp. (browntail moth) or various processionary tree caterpillars (Thaumetopoea sp.).

There are no clear boundaries between the envenoming syndromes described above and they may occur in combination.

Risk

Accidents involving caterpillars have far greater medical significance than those involving adult butterflies or moths. They occur outdoors, predominantly in rural areas, but from time to time also in parks or gardens in the city. In contrast, stings caused by adult animals – in particular Hylesia sp. and Euproctis sp. – often occur indoors, as these nocturnal animals are attracted to the light. Most accidents have a mild course and are limited to local reactions, such that often no medical assistance is sought. Serious and sometimes fatal cases of envenoming have been known to occur in the New World (see below).

Envenoming in humans via skin contact can occur either through touching venomous caterpillars of butterflies or through contact with urticating hairs that float in the air. In the latter situation, symptoms may also arise due to inhaled hairs. The pathological effects are not only caused by the toxic substances involved, but are also due to physical irritation (foreign bodies), with possible secondary infections or allergic reactions.

Numerous accidents occur above all in connection with periodic mass occurrences of caterpillars of venomous species. According to Kawamoto and Kumada (1984), regular epidemic-like outbreaks can be observed amongst members of the following genera:

Automeris

Euproctis

Hylesia

Megalopyge

Latoia

Thaumetopoea

The processionary moths T. pinivorus and T. processionea are members of the mentioned genus Thaumetopoea. Pine processionaries cause considerable damage in the pine forests of the Mediterranean, where they feed on the needles of the trees. 

The asp or puss moth caterpillar Megalopyge opercularis is distributed in Central and South America, as well as in the southern parts of the United States where it is responsible for hundreds of envenomings every year. Envenoming from the spines of the caterpillar occur in the peak months from July through November and can cause severe local pain, burning, swelling, itching, nausea, abdominal distress and headache (Eagleman 2007).

Since the 1990s there have been increasing numbers of reports of severe systemic envenoming following contact with caterpillars of the genus Lonomia in South America. Until the 1980s, accidents caused by these caterpillars were rare. This has continued to change dramatically up to the present, as increasing numbers of non-native settlers move to new farmland that has been generated through the clearing of rainforest, where they then come into contact with Lonomia caterpillars. In particular Lonomia obliqua from southern Brazil and Lonomia achelous from Venezuela and northern Brazil are believed to be very dangerous and are to be considered medically significant animals in these areas. As communal feeders, these caterpillars, like the genera mentioned above, can occur in huge numbers and can thus lead to multiple contacts and application of venom in affected patients. Fibrinolytic proteases and clotting activators have been found in the hairs, spines and hemolymph of these species, which can cause a hemorrhagic syndrome that can progress to acute renal failure, intracranial haemorrhage and death (Veiga et al. 2003).

According to Kowaks et al. (2006), between 1989 and 2005, 354 cases of Lonomia envenoming were reported in the southern Brazilian state of Paraná alone. It was reported that in 1995, 20% of the cases were fatal, while only 1.5% were fatal in 1998. It is stated that the chief cause of death was intracerebral haemorrhage. Similarly severe cases of envenoming have been reported in Venezuela, Ecuador and Peru. The case fatality rate is considered to be 3–6 times higher than for venomous snakebites in Brazil and Venezuela. A specific antivenom against Lonomia obliqua that was developed in recent years at the Instituto Butantan (Sao Paolo) is now available.

Literature (biological)

Delgado Quiroz 1978, Kawamoto and Kumada 1984, Diaz 2005, Kowaks et al. 2006, Veiga et al. 2003

Saturniidae World