Succulent plants tend to have tough leaves and stems rarely troubled by pests. Insects, however, sometimes infest new growth and can cause long-term disfigurement. Small black insects on succulent plants could be aphids or ants associated with them, or hempitera bugs. Indoor potted succulents can also host sciarid flies in their soil.
Black aphids or blackfly infest the young leaves and flower shoots of succulents. They are small, soft-bodied insects up to 1/16 inch long and form colonies. Treat aphids with a spray based on insecticidal soap. Clemson University horticulture specialist Janet McLeod Scott advises testing any chemical on a small section of your plant and leaving it for 48 hours to make sure it is not toxic.
Ants do not damage succulents but may visit them to feed on the nectar in flowers. Ants also feed on a sweet substance produced by aphids and in return, tend aphid colonies and protect them from predators. Remove ants from succulents by treating the aphids that attract them.
Sciarid flies or soil midges are tiny flying insects that live in damp soil and leaf litter. They are not common around succulents because they favor damp soil but can be a nuisance around indoor succulents. Sciarid fly larvae occasionally feed on the roots and lower stems of succulent plants. Treat sciarid flies by allowing the soil around your succulents to dry out and by avoiding peat-based composts.
Hemiptera bugs are small, mobile insects with sucking mouthparts. Several species feed on succulents such as yuccas and cacti. Among them, Hesperolabops gelastop has a reddish colored head and blackish body. It lives in small groups on the upper surfaces of succulent leaves and causes pale blotches up to 1/2 inch across. Some yucca plants have Halticotoma bugs infestations, according to Texas A&M University professor Bastiaan M. Drees. They are 1/4 inch long with dark-gray bodies. Halticotoma bugs live in groups and scatter quickly when disturbed. Treat hemiptera bugs with a systemic insecticide containing dinotefuran or imidacloprid, applied in the spring.