A head for sex?

Species: Thyreophora cynophila

Habitat: Oak forests in central western Europe – on and around dead mammals

This week: a mythical beast, not seen for more than 160 years. A nocturnal animal that feeds on the rotten flesh of large mammals. A species active only during the winter months that reportedly emits a luminous glow from its large, orange head. What new horror is this?


It’s a fly, the bone skipper Thyreophora cynophila, and it is back from the dead. Considered globally extinct until now, the first fly to be killed off by humans, the bone skipper was first described by an entomologist who found it on the carcass of a dog in 1798. Last seen in the 1840s, it has now been rediscovered by Daniel Martín-Vega and colleagues of the University of Alcalá in Madrid, Spain. The fly turned up in baited traps in woodland around Madrid and in La Rioja province.

As might be expected of a species described as “mythical” even by entomologists and that until recently hadn’t been seen in living memory, little is known of its feeding ecology or its behaviour. But we can make some educated guesses.

Big rotters

T. cynophila is sarcosaprophagous: that is, it specialises in eating and breeding in marrow from crushed bones of large mammals such as deer. In the past such carcasses would have been relatively common in European forests after kills by bears and wolves, but these days are scarce.

The decline in large predators coincided with the ecological effects of the industrial revolution: on farms across Europe livestock were better managed and carcasses disposed of in ways that left fewer bones for bone skippers. It is one of the dangers of overspecialisation that when the thing you rely on disappears, you yourself are imperilled – lessons for us all here.

Whether the newly discovered specimens have found something else to feed on and breed in is unknown, as the larvae have not been observed.

Envy the cousins

It would be surprising, however, if they didn’t show the “leaping” behaviour characteristic of this family of flies (the Piophilidae). Bone skipper larvae curl and rapidly uncurl their bodies, thus skipping over their rotten-flesh meal and earning their common name. Larvae of a related fly, the cheese skipper, are only 8 millimetres long but can leap 15 centimetres into the air. These are the maggots, incidentally, that are intentionally added to pecorino in Sardinia, Italy, producing casa marzu rotten cheese.

Martín-Vega and colleagues were studying the colonisation of carrion as part of a forensic entomology study. The Piophilidae are valuable to police in ageing corpses and time of death, as they do not colonise bodies until three to six months after death. Martín-Vega speculates that one of the reasons T. cynophila has evaded entomologists for so long is because collections are not usually made in winter, when the flies are most active. Nor are most entomologists inclined to collect insects from highly decayed corpses.

The bright orange head and blue body of the males suggest that sexual selection is strong in the species, and that like the cheese skippers, bone skippers fight other males and court females. In the 19th century, entomologists impressed by the orange head reported that it could glow in the dark.

Journal reference: Systematic Entomology, DOI: 10.1111/j.1365-3113.2010.00541.x

Read previous Zoologger columns: Even parasitic worms have a divided society, Shrimp plays chicken with its sex change, Death by world’s longest animal, Live birth, evolving before our eyes, Sympathy for the piranha, The world’s most fecund vertebrate, Whale-eater’s helpful sulphur-powered guests, Horror lizard squirts tears of blood, Secret to long life found… in a baby dragon, Eggs with an ‘eat me’ sign.