These pre-historic looking beetles with horns on their head are found under the mulch in your planting beds. They eat decaying plant material, so in order to keep them away from the plants, keep dead leaves out of the garden and pull mulch 3-4 inches away from the plants. They are microscopic parasite worms which are present in the soil and feed on plants. The good ones burrow themselves inside the grubs of some insects in order to reproduce, causing the host insect to die. They do not bother beneficial insects and earthworms in the process.
Bad nematodes can weaken the plants.
Combat these by topdressing plants with compost. This attracts organisms that will in turn attack the nematodes. Fish emulsion also repels or kills nematodes. There are several organic and chemical repellants on the market that claim to repel deer by changing the odor or taste of plants or by making them think there are other predators like coyotes or foxes around. The best, secure way is to build a 10 ft tall fence around the garden.