Sexton beetle's responsible parenthood is rare in the insect world

I received a beetle in the post from Ireland the other day. I don’t think my Gomero postman realised. A reader from Kanturk had sent it, asking me if I might know what kind of beetle it was. 

Sexton beetle's responsible parenthood is rare in the insect world

It had taken some time getting here. It was posted on September 24 and, after being forwarded from my home in West Cork, arrived on this somewhat out-of-the-way Canary island on November 14.

The man who kindly sent the specimen no doubt thought I would have it within one or two days. The delay was nobody’s fault. It arrived in a small envelope, hidden among unsolicited mail which we had told my son that there was no hurry to forward.

When it arrived, it had ripened somewhat, was squashed and had lost its colour. However, the sender had enclosed a good description, and a sketch of what it looked like in life when it was 3cm long, twice as long as it was broad, narrower toward the head and with two striking red bands across its glossy black wing case. He had never seen a beetle like it before.

Neither had the young man and girl who, by coincidence, had contacted me on September 23 (when I was at home) to say they had encountered an unfamiliar, large, black-and-red beetle at Rosslare, Co Wexford. They hadn’t sent the body, but a photo taken with a mobile phone. In both cases, the creatures were clearly members of the burying beetle tribe, (probably Nicrophorus vespillo species). They are commonly called sexton beetles because their role in nature is the interment of small bird and animal carcases which they can, it is thought, detect with their chemical-receptor antennae from over a kilometre away. They do not ring bells or maintain churches, as do human sextons, but they perform a most useful service.

And now we know why we almost never find the remains of a blackbird or thrush in the woods or our gardens, though clearly thousands must ‘fall off the perch’ every day. When a body, pretty robin or hoary rat, is encountered and the first finders don’t have time to inter it before competitors arrive, fights ensue, males against males, females against females and the biggest pair sees the others off before going to work.

There is many a creature buzzing in the air or lurking in the undergrowth that envies them their find. They must make haste to conceal it, but in a very specialised environment if they are to ensure food security and an ideal nursery for their young.

If a female beetle comes alone upon the body, she waits for a male to turn up to mate and produce eggs to hatch into offspring to nurture upon the about-to-be interred. If a male does not arrive, she can fertilise herself with sperm saved from previous couplings. When a carcass is very big (rabbit? duck?) team work will be required. Beetles will assemble, mate and share the labour, and their offspring will share the spoils.

A hole is excavated beneath the body. This is doubled, as much as possible, into a ball from which all hair and feathers are removed, after which it is covered with anti-bacterial, anti-fungal secretions, masking the smell to deceive the competition, and slowing the natural decay. The fur or feathers are used to form a lining for the burial chamber. The interment may take an entire day.

However, when the body is concealed, the sextons’ labours are not yet over. Despite being such grisly actors in nature’s cycle, sextons are very caring parents — although, of course, the motivation is species-perpetuation, with nothing whatsoever sentimental involved.

Before the grubs hatch, the parents make an opening in the carcass to help their new-born offspring reach the tender parts; and then, surprisingly, they respond to ‘begging behaviour’ and will feed the grubs, as birds feed nestlings, although the grubs can feed themselves.

However, the parents are also practical. If the brood is too large to thrive on the food source, they will cull the family, and ensure the survival of the remainder. Sometimes, the carcass would have fed more, probably because the female did not have the time to correctly estimate its food value before laying.

Apart from ants and bees, few insects nurture their young. Unsavoury as the sexton’s job may be, its place in the outdoors is vital. So, now we know where all the dead birds go.

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