Ground beetles number more than 20 000 species. The adults have long legs and long antennae. Most species hide during the day and search for food at night. The adults and larvae prey on other animals. Some species of ground beetles have been introduced to prey on crop-eating insect pests. The bombardier beetle is an unusual ground beetle, defending itself by squirting two chemicals from the end of its body. The chemicals then mix to produce a hot puff of gas that can repel an enemy.