Sluggin' Along: Wedge-shaped Beetles

Wedge-shaped Beetles belong to the family Ripiphoridae. Being parasitoid insects, they undergo hypermetamorphosis. The first instar is typically a campodeiform planidium, a flattened, highly sclerotized and mobile larval form with legs and perhaps eyes, which does not feed. It is phoretic, and thus waits for or seeks out an intermediate vector such as a bee, wasp, wood-boring beetle, or cockroach. When a suitable vector comes along, the planidium attaches itself to the insect and rides back to the nest. Then it enters the body of the larva: the host. Commonly, the planidium will molt shortly after entering the host body. This is called ecdysis and may involve changing its skin and adopting a scarabaeiform (grublike) or vermiform (maggotlike) morphology, thereby losing its legs and eyes, as well as its sclerotization. It will probably postpone further development while the larva grows. As a rule the subsequent instars are of a more or less constant form and not highly mobile, being specialised for feeding and growth until the final instar must metamorphose into the pupal form.

Recently I found two adult specimens of the genus Macrosiagon in my yard. Adults live long enough to mate and lay eggs; then they die. It's uncertain whether they feed. The genus name comes from the Greek meaning "large jaw/cheek, referring to the large maxillae. The elytra of these beetles are long, covering most of the abdomen. The thorax has a projection covering the scutellum. Males and females can be distinguished by the appearance of the antennae and the bluntness of the abdomen.

Here is a male Macrosiagon pectinata (please correct me if I've got the species wrong). You can tell the sex most easily by the feathery antennae. He was resting on a stalk of tall grass within Rosemary.

And this is a female, with serrate antennae. Notice the black color variant and the orangish abdomen. I'm assuming the same species here because I found her in the same general area as the male, but I'm not ruling out an all-black version of M. octomaculatum.