1. Scavengers: Scavengers feed on dead organic matter, such as decaying plants, animals and excrement. Scavengers mainly include some insects, such as dung beetles and ants, carrion sesame insects and pythium.

2. Parasites: Parasites rely on other organisms as hosts to obtain nutrition and energy, and feed on body fluids, tissues or cells in the host. Common parasites include ticks, body lice and parasites.