Blister beetles
Meloidae — chiefly Epicauta spp.
Soft, narrow-necked beetles that arrive in a swarm and strip a row overnight. Never handle them bare-handed: they raise a genuine blister on skin.
How to know it
A soft-bodied beetle 12–20 mm long, narrow and elongated, with a distinctly narrow neck between the head and the body — the shape is the identification. Gray, black, striped or metallic depending on species. They feed in large groups and move along a row together.
What you'll see
- A group of dozens of beetles on a few plants, with everything around them untouched.
- Leaves and flowers eaten out completely, often overnight.
- Damage advancing along the row from one end.
- Beetles dropping to the ground and walking away quickly when disturbed rather than flying.
- Blisters on skin a few hours after handling one bare-handed.
Where it comes from
A strange one. The larvae are predators, hunting grasshopper egg pods in the soil or raiding solitary bee nests — so blister beetle years follow grasshopper years, and the insect is a mixed blessing rather than a straightforward pest. Adults emerge in midsummer and feed in swarms on foliage and flowers for a few weeks. One or two generations a year.
The plains, the west and the south especially, and in the eastern states after a grasshopper year. They arrive suddenly, feed hard for a fortnight, and go.
Dealing with it
- Wear gloves. The beetles contain cantharidin, which raises a real blister on skin and is toxic to horses in hay.
- Knock them into a bucket of soapy water with a gloved hand or a stick.
- Cover the affected row with mesh for the fortnight of the swarm.
- Drive them along the row with a broom into a container rather than trying to catch each one.
- Do not squash them on the plant or on your skin.
Keeping it out
- Cover valued crops with row cover during a known swarm period.
- Keep the garden edges mown, which reduces the grasshopper egg pods their larvae depend on and, indirectly, them.
- Accept them as a short episode; the adults feed for two or three weeks only.
- Never feed garden waste containing blister beetles to livestock, and check hay from a swarm year.
- Remember that the larvae are eating grasshopper eggs, which is a genuine service.
What it goes for
Tomatoes, potatoes, peppers, aubergines, beans, spinach, chard, dahlias and many flowers.
See also
The Cottage Garden Companion — the gardener's bestiary at cottagegardencompanion.com