Sterilise

The use of heat as a sterilising agent is a method of long standing and is particularly effective against most insects. Insects are very susceptible to high temperatures, the ultramaximum temperature—the temperature which will kill an insect instantly—being for the great majority of insects about 140 degrees F. A moderately high temperature, however, if applied for several hours is usually as fatal as a much higher temperature applied for a shorter time.

[…] one tablet completely sterilises a quart of water, tastelessly, without discolouration or odour.

Inspect them for rub marks and blisters; tape or bandage rub marks; clean the skin around a blister, use a sterilised needle to puncture it at its outer edge and press out the fluid, then bandage.

He thinks new classes of insecticides introduced in the last 20 years, including neonicotinoids and fipronil, have been particularly damaging as they are used routinely and persist in the environment: “They sterilise the soil, killing all the grubs.”