Poisonous insects

Ground beetle (Carabus morbillosus ssp. alterans)

Last week a Maltese soldier was hospitalized after he ate a common oil beetle (not in picture) which is also known as a blister beetle. He was not aware that the small black insect was so poisonous as it does not have any particular characteristics that indicate that it is dangerous.

In Maltese the oil beetle is known as dliela żejtnija. 

It is normally found crawling in humid areas feeding on vegetation. Its forewings which in most beetles cover and protect the whole abdomen are small leaving the soft elongated abdomen exposed. Compared to most other beetles that are found in the Maltese islands it is big. The female grows up to 30 mm while the maximum length of the male is 21 mm.

Although it has no distinctive warning markings, sheep and I assume goats seem to be aware of its danger. Shepherds have told me that grazing animals sometimes leave a tuft of vegetation uneaten because of the presence of this beetle. According to them if a sheep eats this beetle it immediately becomes bloated and dies. 

There are records outside Malta of horses accidentally ingesting a blister beetle (not necessarily a species found in Malta) and dying.

The poison, found in this and other related beetles, is known as cantharidin. This causes blistering of the skin and is used to remove warts although its use is not recommended because of its toxicity. 

The poison is generally obtained from a small shiny emerald-green beetle known as Spanish fly which is related to the common oil beetle. The product which is also known as Spanish Fly is given to animals to induce them to mate. Spanish fly has been used by some as an aphrodisiac because during excretion the chemical irritates and stimulates the urethra. 

This is a very dangerous practice as the amount used is very small and the difference between an effective and a toxic dose is very small.

Most toxic animals, especially insects, advertise their toxicity by having warning colours which predators learn to leave alone. Wasps have yellow and black stripes. Ladybirds have black spots on a black background and the great ground beetle (photograph) has a shiny violet body and emits a foul smell when threatened.

Until last week very few people were aware of the toxicity of this beetle. One should keep in mind that this is not the only species of poisonous beetle in the Maltese islands. There are another nine species that belong to the same family in the Maltese islands and they are probably as poisonous as the common oil beetle .

This article was published in The Times on 30.03.2011