The cigarette beetle, Lasioderma serricorne, is a small reddish-brown insect whose larvae feed on tobacco. The unsettling truth about beetles is that their eggs are already present in many cigars before they reach you. Manufacturers freeze finished cigars to kill larvae, but eggs can survive freezing in low numbers and lie dormant in the tobacco for months. They hatch when conditions become favourable.
The conditions that wake them up are warmth and humidity. Tobacconist University, the most cited industry reference, describes beetles becoming active above roughly seventy-three degrees Fahrenheit, particularly when humidity is also high. Eggs do not hatch at fifteen degrees Celsius (about fifty-nine Fahrenheit) at the lower end. The practical advice is the same regardless of where you draw the line: keep your humidor cool, stable, and out of direct heat.
Below seventy degrees Fahrenheit is a sensible target. Above the low seventies, especially with humidity at seventy percent or more, you are making the beetle’s job easier.
If you ever see small holes in your wrappers, pin-prick exit marks at the foot of a cigar, or fine tobacco dust at the bottom of your humidor, you have an active infestation. Remove the affected cigars immediately, freeze the remaining cigars at zero degrees Fahrenheit for seventy-two hours to kill any eggs, and clean the humidor thoroughly before reloading.
The full case on humidity, temperature, and beetle prevention is in How to Rest a Cigar.