Afroagathidium sp. (Coleoptera: Leiodidae: Leiodinae: Agathidiini)
Our insect of the week (53) is a species of leiodid beetle of the tribe Agathidiini, probably Afroagathidium sp. Leiodidae is a large family comprised mostly of very small to small beetles with around 3800 species worldwide. Members of this family are commonly called round fungus beetles due to the globular shape of many species, illustrated nicely by this week’s insect. They are one of the many groups of saprophytic insects whose primary ecological function is to break down decaying organic matter into its constituent states. This vital behaviour recycles essential nutrients back into the environment. The subfamily Leiodinae is a large one, although poorly represented in the Afrotropical region, with about 40 species distributed among 5 tribes and 13 genera. Agathidiini, the largest tribe of the subfamily includes about 11 genera and 950 species, but comparatively little is known of species’ numbers and their distributions in the Afrotropics. Our species was collected in Suam Forest in western Kenya at an elevation of 2324m above sea level.
Insects have evolved many defensive strategies, including aposematic (warning) colouration, mimicry, camouflage, a spiny integument and the release of noxious chemicals. However, some Leiodidae have a different way of defending themselves. Members of several agathidiine genera are capable of conglobation (a nice word meaning the ability to roll oneself up into a ball-like shape). This behaviour helps to protect the vulnerable undersides from attack by predators. Among the conglobating Agathidiini are species of Afroagathidium and Agathidium. Some unrelated insects also use conglobation for defence such as species of the tiny jewel wasp genus Holophris and those of the pollen-collecting wasp genus Celonites (Masarinae). Other, more familiar animals such as the armadillo and hedgehog, also use this method of defence.
Agathidiini feed on slime moulds (Myxomycetes), a crazy taxon whose affinities were difficult to discover, so that historically they have been placed in the fungi by mycologists and as amoebae by zoologists. Presently they are considered a separate phylum (Mycetozoa) in the kingdom Amoebozoa. They have a complicated life cycle that includes amoeba-like motile forms, and fruiting bodies that resemble fungi. Typically, the fruiting body forms because of environmental stress (e.g. food-limitation or climatic changes [e.g. increasing aridity]). Fruiting bodies are often beautiful, sometimes not, as the aptly named “dog vomit” fruiting body illustrates.
Credits: Dr Robert Copeland