Ephydridae is a family of insect

Insect

Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...

s in the order Diptera

Diptera

Diptera , or true flies, is the order of insects possessing only a single pair of wings on the mesothorax; the metathorax bears a pair of drumstick like structures called the halteres, the remnants of the hind wings. It is a large order, containing an estimated 240,000 species, although under half...

.

Shore flies are tiny flies that can be found near seashores or at smaller inland waters, such as ponds. About 1,500 species have been described worldwide.

The petroleum fly

Helaeomyia petrolei

The petroleum fly, Helaeomyia petrolei, is a species of fly from California, USA. The larvae feed on dead insects that become trapped in naturally occurring petroleum pools, making this the only known insect species that develops in crude oil, a substance which is normally highly toxic to...

, Helaeomyia petrolei, is the only known insect whose larva live in naturally occurring crude petroleum

Petroleum

Petroleum or crude oil is a naturally occurring, flammable liquid consisting of a complex mixture of hydrocarbons of various molecular weights and other liquid organic compounds, that are found in geologic formations beneath the Earth's surface. Petroleum is recovered mostly through oil drilling...

.
See Family description and images
In the subfamily Notiphilinae the head is reduced to a cephalic skeleton, there are no anterior spiracle

Spiracle

Spiracles are openings on the surface of some animals that usually lead to respiratory systems.-Vertebrates:The spiracle is a small hole behind each eye that opens to the mouth in some fishes. In the primitive jawless fish the first gill opening immediately behind the mouth is essentially similar...

s and the posterior spiracles are extended as spines.
The other subfamilies have larva

Larva

A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...

e similar to the Sciomyzidae

Sciomyzidae

The family Sciomyzidae belongs to the typical flies of the order Diptera. They are commonly called marsh flies, and in some cases snail-killing flies due to the food of their larvae....

, with the posterior spiracles at the apices of divergent branches from a common base.