The short answer for a leopard gecko
A leopard gecko can have hornworms, silkworms, and black soldier fly larvae as treats, offered a few at a time within one or two feeds a week. These insects suit a leopard gecko because it is a dedicated insect hunter, and a soft, slow hornworm or a wriggling silkworm triggers a focused stalk that staple feeders sometimes do not. Waxworms sit in a stricter category for a leopard gecko: one or two, rarely, because their fat content and appeal can spoil the gecko's appetite for everything else.
Why insect variety matters to this gecko
A leopard gecko hunts by sight and movement on the ground at dusk, tail raised and twitching as it closes on prey. New insect shapes and movements exercise exactly that behaviour, and softer treat insects also bring extra moisture, which suits a leopard gecko from dry rocky country that takes much of its water from food. The risk runs the other way from many pets: a leopard gecko stores fat in its tail, so a treat habit shows late, and by the time the tail looks overly plump the gecko may already be refusing the staple insects it actually needs.
Treats that suit a leopard gecko
A small hornworm is the star treat for a leopard gecko, soft, hydrating, and slow enough for an easy catch, though they grow fast, so buy small and use them promptly. Silkworms are gentle, nutritious treats a leopard gecko can have a little more freely within a treat feed. Black soldier fly larvae add a calcium-rich crunch, and an occasional butterworm gives colour and scent variety. Every treat insect for a leopard gecko should be gut-loaded and dusted as staple prey is, and sized no wider than the space between the gecko's eyes to keep swallowing safe.
How often, and how many
For an adult leopard gecko, fold treats into one or two of its weekly feeds rather than adding separate treat sessions, keeping staples as most of every meal. A sensible pattern is a couple of treat insects first, while the leopard gecko is keen, then staple feeders to finish. Juveniles eat daily and grow fast, so their treats should be smaller and less frequent, with staple insects dominating. If a leopard gecko starts leaving crickets untouched while hunting hopefully for waxworms, drop waxworms entirely for a few weeks until the staple appetite returns.
Watch-outs for a leopard gecko
Check a leopard gecko's tail shape and hunting enthusiasm together: a healthy tail is plump but not bulging, and a gecko that suddenly ignores all insects needs attention beyond menu changes. A leopard gecko with a thinning tail, stuck shed on the toes, drooping posture, or repeated regurgitation should see a reptile vet, as should one whose belly shows dark shadowing through the skin after a very large treat insect. Never offer wild-caught insects to a leopard gecko, since garden insects may carry pesticides or parasites that captive feeders avoid.
Tracking treat feeds in a busy household
A leopard gecko fed by two or three people can receive waxworms from each of them in the same week, each keeper thinking theirs was the rare treat. One shared list ends the guesswork. Using KinsLe Care Teams, you can put the treat feed on a named day, mark it complete when the insects are given, and leave staple-only feeds clearly marked for this gecko on the other days.