|October 2016. Beetles were sent for identification to the Australian Museum from Pohnpei, the Federated States of Micronesia.
They are invading schools in Pohnpei and causing blisters on the arms and legs of children. There have been posts to Pestnet on these kinds of beetles in the past, from FSM and other parts of the Pacific.
http://www.pestnet.org/ SummariesofMessages/Pests/ PestsEntities/Insects/Beetles/ Sessinialivida,FSM
http://www.pestnet.org/ SummariesofMessages/Pests/ PestsEntities/Insects/Beetles/ Tenebrionids/ Morefalseblisterbeetles, CookIs
In response, Chris Reid from the Museum said the following:
It is a member of the Oedemeridae, genus Copidita. There are many species in Australia and they occurs widely in the Pacific. They breed in wood (e.g., a cosmopolitan pest, Nacerdes melanura, is a pest of wharves and marine timbers; the present beetle is probably doing something similar). Oedemerids can contain the chemical cantharidin, which is very toxic (https://en.wikipedia.org/ wiki/Cantharidin) – this may have caused the blistering on the children.
A key feature of Oedemeridae (and showing in your photos is the lobed 4th tarsal segment). Larvae look like wireworms (long, cylindrical, with short legs, but are creamy white). The larvae are infesting timber, especially that has been infected by white rot – someone needs to check timber sources such as decking, walls, ceilings, maybe part buried wood outside. Anything that has started to rot. It may be a building construction fault since you have several different buildings involved. The adults seem to be polyphagous, but are mostly on flowers. They are also attracted to lights – its also possible that these buildings have lights left on and beetles are flying in from rotting timber.
Another member from Pohnpei added to the discussion by saying that he had been observing blister beetle outbreaks for several years in Pohnpei. It is usually this time of the year (September/ October), they come in thousands, ceilings are covered and they cause blisters when disturbed. We receive many reports from schools, and they ask us what to do.
I tell them to turn off the light at night and try to smoke them out. As a last resort a contact pesticide can be used. Once we had to spray three or four times to get the beetles under control. I wonder what can be done to prevent the build-up of the beetle.
A member from Palau wrote: I get something like this in my house from time to time. There can be dozens, maybe even hundreds of the beetles, crawling on walls and ceiling. This will go on for a few days, and then they all disappear (until the next time). I am told they are a blister beetle. They are really a nuisance if I am using the computer in the evening, because they are attracted to the screen. They have never caused blisters, though, on me or any members of my family.