Thriving colonies of antlions discovered in Norfolk nature reserve
Latest survey confirms Holkham as only the second breeding area in Britain for rare insect predator.
Staff at Natural England’s Holkham National Nature Reserve have discovered what is thought to be only the second established breeding area in Britain for the mysterious yet savage antlion, an insect whose larvae excavate cone-like pits and lurk in wait for other insect prey. And its numbers on site appear to be increasing.
Antlion species © Mike Richardson, from the surfbirds galleries.
There had been reports of antlions skulking in the sandy ground beneath the Reserve’s pine woods since 2005, but there was uncertainty about the exact species and numbers involved. In 2008, Reserve staff undertook a full survey of the site to identify the species and determine the size and distribution of any population. This survey discovered just over 700 larval pits and confirmed the species as Euroleon nostras, but the scarcity of this insect in the UK meant there was always the chance this could be temporary colonisation. This year a further survey was carried out and found no fewer than 1,905 larval pits, confirming not only that the colony was still present but had almost trebled in size.
Although the adults look like small dragonflies, antlions are members of the lacewing family and are chiefly known for their ferocious young. The larvae’s prey includes ants, woodlice and other small invertebrates. Any insect unlucky enough to wander over the rim of the cone shaped burrow finds itself sliding inexorably down the steeply angled, shifting sand. At the bottom it is seized in the ant-lion’s huge jaws and sucked dry. The larvae live like this for two years before pupating into flying adults in late summer. Like other lacewings, the adults lead much briefer lives than their young – less than a month.
Holkham NNR is such a suitable site for the antlion because it has open banks of sand for the larval pits, abundant prey and pine trees, where the adults mate.
Natural England’s Senior Reserve Manager, Michael Rooney said “We’re really pleased with what the two surveys revealed: that the antlions are thriving at Holkham, with a sizeable population spreading through the pine woodland. It will be interesting to see what will migrate north to Holkham next.”
The only other known breeding area for the very rare antlion is the Suffolk Sandlings and the confirmation of an established breeding area in Holkham is another great success for the Reserve, which also hosts Britain’s only breeding spoonbill colony.
Euroleon nostras is a species of antlion found over most of Europe, but is extremely rare in Britain. Adults may reach up to 30 mm long, with a wingspan of 70 mm, and larvae are around 10mm. The larvae require dry sandy soil to dig their pits, close to vertical sandy ledges that help adults emerge. Larval ant-lions have such efficient digestion that they do not produce solid waste and therefore do not need an anus. Larvae exude only liquid waste; the small amount of solid waste that may build up is excreted by newly emerged adults. Antlions remain in their larval stage for two years before pupating. Adults emerge from the pupa towards the end of July or in the first few days of August. They gather in a tall pine tree, and a number of males attempt to attract a single female. After mating, the female flies to the ground, where she lays her eggs in the sand. She has to be particularly wary of ant-lion larvae at this time, which are the main predators of female adults. Males live for up to 20 days, while females last a little longer, with an average life span of 24 days.