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THE NEW ZEALAND
MEDICAL JOURNAL
Vol 119 No 1241 ISSN 1175 8716
NZMJ 8 September 2006, Vol 119 No 1241 Page 1 of 6
URL: http://www.nzma.org.nz/journal/119-1241/xxxx/ © NZMA
Erucism in New Zealand: exposure to gum leaf skeletoniser
(Uraba lugens) caterpillars in the differential diagnosis of
contact dermatitis in the Auckland region
José Derraik
Abstract
There are no indigenous caterpillars known to be associated with erucism, but the
recently established gum leaf skeletoniser (Uraba lugens) has venom-containing
spines that cause adverse reactions in humans. Symptoms are usually characterised by
a stinging sensation, followed by itching and the formation of wheals. Exposure to
U. lugens should be considered by medical practitioners in the differential diagnosis
of contact dermatitis in the Auckland region.
Introduction, biological notes and distribution
‘Erucism’ is the term generally used to refer to the adverse reactions resulting from
contact with urticating caterpillars, the larval forms of the insect order Lepidoptera
(moths and butterflies).1,2 Although erucism is a relatively common public health
problem throughout the world,1 there are no indigenous species of Lepidoptera in
New Zealand whose caterpillar is known to cause adverse reactions in humans (Brian
Patrick, Otago Museum, personal communication; 2006).3 As a result, erucism has
never been a human health issue in this country, and is therefore a condition
somewhat unknown to local medical practitioners.
The situation has changed however, since the establishment of the gum leaf
skeletoniser Uraba lugens Walker (Lepidoptera: Nolidae), an Australian moth whose
caterpillar feeds on the foliage of gum trees (Eucalyptus) and other closely related
genera.4 The younger larvae avoid feeding on the oil glands and veins found in the
leaves, which are consequently ‘skeletonised’.3 More mature larvae will however eat
the whole leaf.3
Uraba lugens is a significant pest for Eucalyptus forestry. Infestation by U. lugens
may kill young trees if there is repeated defoliation.5 This process on larger trees may
reduce wood production for several seasons.6 Outbreaks of this species seem to
periodically occur in natural forests in Australia, but these eventually recover, even
though defoliation can be severe.7
Uraba lugens was first discovered in New Zealand in 1992, and it is now firmly
established in the Auckland region, over an area of at least 20,000 ha.4 Due to its wide
distribution, eradication was deemed to be not feasible.8 Uraba lugens is now the
focus of a long-term management programme aiming particularly at filling current
knowledge gaps and controlling the existing population.8
The approximate distribution of U. lugens currently goes as far north as Takapuna and
as far south as the Bombay Hills, including the area between the Hunua Ranges in the
east and the Manukau Heads and Waitakere Ranges in the west.7 The highest density
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of this organism seems to occur in southwest Auckland.9 Results from climatic
models indicated that U. lugens could potentially establish throughout New Zealand.
To date, the population is not known to be established outside the Auckland region,
but specimens have recently been captured in pheromone traps in Katikati (Bay of
Plenty) and Warkworth (Northland).18
The Auckland populations of U. lugens have two generations per year (bivoltine),
with larvae usually present from January to March (summer) and May to October
(winter).10 Uraba lugens caterpillars vary in length from 1 to 25 mm depending on the
stage of development.3. There are between 11 and 13 larval stages.4,5
Uraba lugens are extremely hairy caterpillars with yellow and brown markings, and
when mature they retain the head capsules of previous instars that are pushed up to
top of the head, which makes U. lugens easy to identify (Figure 1).5 Each body
segment of the larvae has 10 tubercles, four of which are located dorsally and have
short, stiff, brown-tipped bristles that are hollow and contain venom that can be
injected into the human skin upon contact.3
Figure 1. Uraba lugens caterpillars (Photo courtesy of Ensis)
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Exposure, symptoms of envenomation, and possible treatment
The exposure of people to stinging caterpillars is greater when these creatures are
occurring at high densities, as numerous caterpillars may be found in the direct
vicinity of an infested tree. Large infestations of stinging caterpillars can become a
serious public health issue, and in some severe cases it has led to the closure of
schools.2
Figure 2. Wheals formed approximately 30 minutes after exposure to the
urticating spines of Uraba lugens (Photo courtesy of Ensis)
Most cases of harmful exposure to caterpillars seem to occur in young children, and in
one study of 365 cases of exposure to Lophocampa caryae Harris (Lepidoptera:
Arctiidae), 80% of the records were paediatric exposures.11 Caterpillars are a source
of curiosity to children due to their easy accessibility and slow mobility,11 and also
due to these creatures’ generally bright colours. Young children tend to have thinner
skin and smaller bodies than adults, both of which may increase the extent of the
reaction.12
Approximately 150 species of Lepidoptera from more than a dozen families have
been described to cause some form of injury to humans.1,13 The caterpillars of many
species have chitinous spines that are capable of penetrating human epidermis, and
injecting venom parenterally.13 Exposure to stinging caterpillars can result in a variety
of reactions, which vary according to the species,14 but adverse reactions range from
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moderate to severe local effects, usually characterised by severe pain, and less
commonly systemic effects,14 including renal failure and intracerebral hemorrhage.1
The nature of U. lugens venom is largely unknown,12 but it contains histamine and
most likely also a proteinaceous substance.3 Skin contact with the envenomating
bristles of U. lugens will immediately cause a sharp stinging sensation, which may be
severe.3 Local pain is followed by the associated formation of flat itching wheals
(Figure 2),15 which may remain visible for a few weeks.3
The skin reaction may cause a high degree of discomfort, and an adult woman
described the reaction as “violent and distressful for 3–4 days”.3 As a result, adverse
reactions to U. lugens venom may be particularly distressing for young children. It is
important to note that even the spines on the youngest caterpillars are capable of
stinging, and that these continue to sting even after the insect is dead, and also
following the shedding of skin.3
Ingestion of caterpillars of other species by children has been described in the
literature,1,14,16 with some adverse effects consisting of pain, difficulty swallowing,
drooling, and shortness of breath.16 There seem to be no records of U. lugens
ingestion, but it would be likely to require hospitalisation. While life-threatening
reactions are unlikely to occur, the possibility of serious adverse reactions, such as
anaphylaxis, cannot be discarded.12 Although severe and systemic reactions to
U. lugens have not been described, eye lesions could be potentially serious and should
be dealt with by a specialist. Note that there is no evidence of sensitisation from
repeated exposures to U. lugens.3
Contact with some caterpillar species such as the white-stemmed gum moth
(Chelepteryx collesi) leads to a very large number of hairs becoming embedded in the
skin.17 Even though for some species attempts to remove the hairs seem to be
unsuccessful,17 the careful removal of spine(s) with adhesive tape is a commonly
prescribed initial treatment of urticating caterpillar stings.2,14 However, this is not
likely to be an issue with U. lugens, as there seem to be no reports of its spines
becoming embedded in human skin, especially in Southcotts’s detailed descriptions of
numerous cases of exposure.3 Instead, the application of ice packs, and oral or topical
administration of antihistamines to attenuate itching and burning sensation, is
advised.1,2,14 Intense inflammatory reaction may be locally relieved by topical or oral
corticosteroids.1,2
Current incidence and recommendations
There are no available data on the incidence of exposure to U. lugens in New Zealand.
Biosecurity New Zealand has information on at least two confirmed cases, where
members of the public have contacted the agency following adverse reactions to an
‘unknown’ caterpillar (Mark Ross, personal communication; 2006). However, based
on the distribution of the caterpillars in the Auckland region and its relatively high
density in some areas, one could expect the actual number of cases to be considerably
higher. The author would welcome information on any confirmed cases of exposure
to U. lugens in New Zealand.
Even though U. lugens is the target of a long-term management programme, this
species is well-established in the Auckland region and will not be eradicated. Since
Auckland is the most populated region in the country, human exposure to the
NZMJ 8 September 2006, Vol 119 No 1241 Page 5 of 6
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caterpillars is likely to occur on a regular basis, particularly among children. As a
result, general practitioners should consider exposure to U. lugens in the differential
diagnosis of contact dermatitis, where symptoms such as wheals are present.
Prevention is an important tool, and in cases where exposure to U. lugens is
confirmed, the access of children to areas adjacent to infested trees should be
restricted, and a reputable pest controller should be contacted for mitigating action. In
case the infested tree is located on public land, the local or regional authority should
be notified.
Avoidance is a fundamental preventive tool, and children should be educated not to
touch or handle U. lugens caterpillars. It should be also noted that this species’
potential establishment in Eucalyptus plantations in New Zealand may lead to
occupational safety and health concerns, as a result of the likelihood of exposure to
forestry workers.12
Author information: José G B Derraik, Advisor (Human Health), Risk Analysis
Group, Pre-Clearance Directorate, Biosecurity New Zealand, Wellington
Acknowledgements: I thank John Fountain (National Poisons Centre, University of
Otago), Doug Lush (Ministry of Health), and Ian Gear and Mark Ross (Biosecurity
New Zealand) for revising this manuscript and providing valuable feedback.
Ensis Forest Biosecurity & Protection has kindly allowed their photographs to be
included in this article. Thanks also to Brian Patrick (Otago Museum) for input.
Correspondence: José G B Derraik, Biosecurity New Zealand, PO Box 2526,
Wellington. Fax: (04) 894 0733; email: jose.derraik@maf.govt.nz
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