The Cleridae Latreille 1802, known commonly as ham beetles or checkered beetles, are a family of brightly-coloured and hairy predatory beetles, measuring between 3 and 12 mm. They’re easily recognisable by having a narrow pronotum (“neck”), with both the head and the wing bases being wider than it. Clerid larvae are recognisable by having strongly ventrally protracted mouthparts.
The Thanerocleridae are often treated along with the Cleridae due to their similarities, however it is agreed that they are different families within the Cleroidea superfamily (Kolibáč, 1992), a superfamily that also includes the monogeneric Metaxinidae (Kolibáč, 2004) and a host of other families, the relationships between which aren’t quite cleared up yet. What is fairly certain is that the Cleridae, Thanerocleridae and Chaetosomatidae are sisters. The other certain clade is the Melyridae, Acanthocnemidae and Phycosecidae clade (Lawrence & Newton Jr., 1982). Other families in the Cleroidea include the Phloiophilidae, Trogossitidae and Prionoceridae.
The Thanerocleridae are predators, digesting their prey extraorally. They have very secluded lifestyles, dwelling on tree-growing fungi, in termite nests, or in stored products. They’re impossible to collect in Europe, as none have been found here yet. But they are present on every other continent (except Antarctica), including Australia.
The Cleridae themselves contain over 4000 species in 300+ genera (Gerstmeier, 2000) sorted in seven subfamilies (Lawrence & Newton Jr., 1995), although as always in entomological classification, this system is in flux and in my opinion, we would be better off getting replacing the seven subfamily system with the 12 subfamily system proposed by Opitz (2010). Note that in the latest nomenclatoral catalog for beetle families, a four subfamily system is promoted for the Cleridae, with the three remaining subfamilies demoted to tribe status (Bouchard et al., 2011). So as I said, it’s pretty much up in the air for now. Also as usual, the highest diversity is in the tropics, with relatively few to be found in the colder latitudes.
The phylogeny of the Cleridae is in need of revision. One curious hypothesis of their evolution is the association of monophyletic spermatophore-producing clerid genera all being uniquely flower-visiting and nectar-feeding; it’s hypothesised that the move to a relatively poor diet stimulated the production of spermatophores by the males in order to provide the females with more nutrients (Opitz, 2003).
Of the seven subfamilies, the Clerinae is the most speciose, containing nearly half the species, most in the Afrotropics (Gerstmeier, 2000).
As predators, they are often used as biocontrol, most often of bark beetles (adults or larvae) and most successfully of the Douglas-fir beetle (clerids used: Enoclerus sphegeus and Thanasimus undulatus). There is even an example of clerid predation driving the evolution of bark beetles. Ips pini, the bark beetle in this example, uses aggregation pheromones to get together and initiate mating. Their clerid predators can detect these as well, if not better, than the bark beetles themselves (Hansen, 1983), so they go to the meeting place and slaughter the bark beetles. This has led to natural selection acting on the pheromone in local populations, slightly changing its chemical composition to make it less detectable by the clerids (Raffa & Dahlsten, 2005). But this has also led to it being less detectable by members from more distant populations (Aukema et al., 2000). This is the first step twoards reproductive isolation and eventually, speciation.
Another cool ecological phenomenon involving clerids is that described by Letourneau (1990). In this case, the clerids act as parasites of a plant of the genus Piper in the tropics. Usually, the plant is in a mutualism with ants: the ants defend the plant, the plant rewards them with food; the food is costly to produce, so the plant only makes it when it detects the ants on it. What the clerid does is kill the ant colony on the plant; somehow, it fools the plant into continuing to think that it has ants on it, so the clerid keeps getting the nutritious reward, at the cost of the plant’s physiology.
Speaking of clerids and plants, some adults are pollen-feeders instead of predators, and these species are prominent pollinators, as far as beetles go. The larvae are almost always scavengers.
Those who want to collect them, from personal experience, I can say that window traps work best for them, either hanging freely or on a tree trunk. A good bait is ethanol, as they tend to be attracted to fermentation products of tree resins (Montgomery & Wargo, 1983). Active collecting can be done on foliage, flowers or dead tree barks. One genus, Necrobia, is also a common stored-product pest (making it one of the most widespread of the clerids; as an example, it was the first insect accidentally introduced to the Galapagos islands back in 1535 on Bishop Thomas de Berlanga’s trip there, along with cockroaches). It’s easily found in dried meat left out for too long.
Related to that, clerids can be necrophagous and can be found in carrion (Braack, 1981), so they also have utility in forensic entomology (Haskell et al., 1997). As a general rule of thumb, they come when the corpse has dried, found in conjunction with dermestids, nitidulids, trogids, tineid larvae, ants and mites. Most famously, this type of assemblage has been found by Egyptiologists on mummies (Huchet, 1995). They feed on the keratin, and clear any hair or feathers remaining on the corpse. In some exceptional cases, especially in hot areas, they can be found when the carcass is bloated, i.e. in the early stages of decay, at which time they feed on dipteran larvae and muscle tissue.
Being generally colourful beetles, some clerids engage in mimicry (Mawdsley, 1994). Many resemble other beetles, while some go for an ant-shape (Hespenheide, 1986), while some might even go for mimicking wasps – sometimes so successfully that they cause us to rethink how we distinguish the mimicked species. This was the case of Trogodendron fasciculatum, a very good mimic of pompilid wasps (Faithfull, 1994). Often, these mimicries are part of larger mimicry complexes involving members of other beetle families.
Clerid larvae are active predators, even going as far as entering ant nests to hunt (Berryman, 1966). They can be collected in leaf litter.
Fossil record-wise, they’re found in both amber (see Spahr, 1981) and rocks (e.g. in Eckfeld). Opitz (2007) is the most recent review of fossil clerids, although it was focused on the old literature and several papers have been published since 2007 anyway.
They’re also fairly prominent subfossil, especially for Egyptologists. Being partly necrophagous, several have been found on mummies. Necrobia rufipes, for example, was found on the mummy of Ramses II (Steffan, 1982).
Most interesting about their fossil record is a Baltic amber specimen preserving several mites phoretic on a clerid beetle (Weitschat & Wichard, 1998). It’s another instance of parasitism preserved in the fossil record.
Finally, to round the post off with interesting trivia: the clerid Divales bipustulatus has spermatozoa that are 1 cm long (Mazzini, 1976), to my knowledge the largest sperm among the beetles (and probably ranks near the top in the insect world, if not among all animals, but I have no data to back these up).
The most prominent clerid specialist in the world is Weston Opitz, so if any reader wants to specialise in them in the future, he’s the one you should suck up to.
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Letourneau, D. (1990). Code of Ant-Plant Mutualism Broken by Parasite Science, 248 (4952), 215-217 DOI: 10.1126/science.248.4952.215
Hansen, K. (1983). Reception of bark beetle pheromone in the predaceous clerid beetle,Thanasimus formicarius (Coleoptera: Cleridae) Journal of Comparative Physiology ? A, 150 (3), 371-378 DOI: 10.1007/BF00605026