antlion larva; doodlebug
Refers specifically to the larval stage of the antlion (family Myrmeleontidae), known for digging conical pits to trap ants. The adult insect is called ウスバカゲロウ.
See also: ウスバカゲロウ
Antlion larvae make funnel-shaped pits in sandy soil.
The child is dropping ants into the antlion pit and watching.
antlion pit
The conical pit trap itself, often found in dry, sandy soil. Can also be used figuratively for a situation from which it is hard to escape.
Several antlion pits had formed under the eaves.