Garrards: Service with integrity

High school students in the Brisbane area found a unique way to avoid school.  In the first six weeks of school in 2008, 52 students were told to go home and eight of these sought medical treatment.  The students complained of being ‘bitten’ in several areas of the grounds.  They had seen hairy caterpillars on a table but investigation around that area showed nothing.  The school called out a pest management company, they checked the wattle trees which are a known home for the bag shelter moths – but they did not find any.  However, the stinging (urticating) hairs of caterpillars were the most likely cause – so where were they?

The easiest way to find the infested trees is to look for damage to the newest leaves.  The photo shows the lack of leaves around the perimeter of the foliage (skeletonizing).  The bags and caterpillars were then found on the trunk about fine metres above ground level.  Other trees of a similar type were checked – all twelve had masses of caterpillars and directly coincided with the areas of complaint.

A pest management company removed the caterpillars and treated the trees using a cherry picker.

Note the nests on two trunks of the tree.

Hairy caterpillars are not confined to coastal areas.  Inland trees may also be attacked.  In April, a pest manager noted the cast off skins and webbing of hairy caterpillars on trees in Moree while carrying out a timber pest inspection..  He asked the staff that worked in the office nearby if they had experienced ‘itches’.  “Yes, in the new year some people complained but we thought it was ….”  The pest manager’s insight impressed the client and now he has a job booked in for each November.

The skeletonizing of ‘mongrel’ cedar trees by caterpillars in Moree.

There are various species of caterpillars with stinging hairs.  The biology is similar, the caterpillars overwinter in a cocoon, pupate in spring, emerging as a moth several weeks later.  The larva feeds on the leaves of selected trees as they go through up to eight moults.  If they eat out one tree they leave en-masse in single file – hence the term processionary caterpillar – and find another.

All stages of the life cycle – eggs, larvae, cast larval skins, pupae and adults – and the bag shelter have irritating hairs and can cause dermatitis.  The hairs are tapered, barbed, and easily penetrate skin releasing a poison when they break which causes an itchy dermatitis.

The White Cedar Moth attacks White Cedar (also known as Cape Lilac) trees.

The Queensland Museum has a fact sheet on “Bag-shelter Moths and processionary caterpillars” available at www.qm.qld.gov.au.