On many worlds, the biomass of insects radically outweighs that of higher organisms. Mass migrations and deadly insect species can imperil larger creatures, but most insects remain nothing more than an annoyance. However, through wild population booms, magical manipulation, supernatural growth, interbreeding with otherworldly species, or stranger circumstances, insects can overrun an entire region. Swarms of insects become the dominant species in an area, consuming plants and animals, creating elaborate hives or tunnels, and infesting structures and the earth.
The following effects represent a region overrun by insects or hives of similar creatures, likely manipulated by magic, otherworldly intelligence, or environmental factors to infest an area in countless numbers and drive out all competing life.
Consider rolling on the Infested Effects table when the following circumstances occur in the region:
| Infested Effects | |
| d100 | Infested Effects |
| 01-05 | Intense buzzing or grinding noises fill the region for the next 24 hours. With the exception of truly cacophonous sounds, creatures can only hear speech and noises that originate within 10 feet of them. |
| 06-10 | A mass migration of insects begins, with waves of Tiny bugs crawling over everything in the region. Creatures cannot take a Short or Long Rest in the region for the next 24 hours. |
| 11-15 | A swarm of bioluminescent flies converges on one random creature in the region. For the next minute, the creature sheds dim light in a 10-foot radius, any attack against it has advantage if the attacker can see it, and the creature can't benefit from being invisible. |
| 16-20 | A boil of termites bursts from the ground, along with dozens of bones and a treasure of the DM's choice (see "Random Treasure" in the Dungeon Master Tools section). |
| 21-25 | A cricket-shaped creature with the statistics of a cat bounds up to one random creature and follows it like an affectionate pet for 24 hours before scampering off. |
| 26-30 | A cluster of 1d4 + 2 faintly glowing grubs appears in an unoccupied space within 30 feet of the party. Any creature that consumes one of these succulent grubs receives the benefits of a potion of healing. |
| 31-35 | A large, psychedelically colored moth flies over the party, dusting the characters with strange powder. Creatures the moth flies over must succeed on a DC 16 Constitution Saving Throw or be charmed by all creatures for 1 hour. |
| 36-45 | The region is choked with wispy webbing, which acts as difficult terrain. |
| 46-50 | Nearly every surface is covered with discarded cicadae-like shells that crunch loudly when trod upon, imposing disadvantage on Dexterity (Stealth) checks made while moving across them. The shells vanish after 1 hour. |
| 51-55 | A massive, bloated maggot emerges from the ground within 10 feet of the party and bursts, covering the ground with ichor in a 10-foot square centered on it. This region is affected by the Grease spell (save DC 13) for 1 minute. |
| 56-60 | The ground opens up beneath one random creature, creating a quicksand pit. |
| 61-65 | One random creature in the region must succeed on a DC 16 Constitution Saving Throw or contract the sight rot disease from minute parasites. |
| 66-70 | Dung-colored bugs cover the ground. Creatures that move at half their normal walking speed can ignore the bugs. Those that move faster must succeed on a DC 16 Constitution Saving Throw or become poisoned until the start of their next turn. A creature poisoned in this way has its speed reduced to 0, as it is overcome by the squashed insects' foul smell. Creatures that don't need to breathe automatically succeed on this saving throw. |
| 71-75 | One of the characters in the region must succeed on a DC 15 Wisdom Saving Throw or be transformed into a giant spider, as if by the Polymorph spell. The spell lasts for 1 hour or until dispelled. |
| 76-80 | One random creature in the region must succeed on a DC 16 Constitution Saving Throw, or it acquires a ravenous silverfish infestation among its gear. The infestation is discovered the next time the creature finishes a Short or Long Rest. If the creature has any paper material, the silverfish destroy one random book or other paper item that isn't magical. |
| 81-85 | One random creature in the region must succeed on a DC 16 Constitution Saving Throw or become host to a particularly aggressive tapeworm. The affected creature gains no benefit from eating until it receives treatment that removes a disease. A creature immune to disease automatically succeeds on this saving throw. |
| 86-90 | Biting mites infest creatures' clothing in the region. Any creature wearing medium or heavy armor has disadvantage on Attack Rolls, Ability Checks, Saving Throws for the next 24 hours. |
| 91-95 | Tiny arachnids invade unattended spaces. The next time one random creature in the region dons its clothing or armor after finishing a long rest, it must succeed on a DC 16 Constitution Saving Throw or take 11 (2d10) poison damage. |
| 96-00 | Countless tiny, bloodsucking insects infest the region for the next 1d6 hours. Every hour, each creature in the region must succeed on a DC 10 Constitution Saving Throw or gain 1 level of exhaustion. The insects don't affect creatures that are immune to disease. |