VCSU Macro-Invertabrate Lab
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Order Ephemeroptera

Key to Mayfly larvae. There are ten Families of Ephemeroptera that have been collected in North Dakota rivers and streams. We have broken down those ten Families into four groups. Examine the descriptions and pictures shown below and decide which group your specimen best fits. Group One consists of a single Family. For the other three groups, click on the link for that section and you will go to another page that will break that group into families.

Family Baetiscidae - Notum expanded into broad shield that covers thorax and part of the abdomen (Fig. 1). This shield usually has a prominent points on each side.

Baetiscidae shield
Group One- Mayflies with mandibular tusks. These mayflies have elongated tusks that project forward in front of the head (Fig. 2). Three Families - Polymitarcyiidae, Ephemeridae (including Palingenidae), and Potomanthidae (Fig. 3).

Polymitarcyidae head Potomanthidae body
Group Two - Sprawling type mayflies. These mayflies usually have a fairly compressed appearance. Their legs are usually splayed out to the side (Fig. 4). Some may have operculate gills on the second abdominal segment. Families Caenidae (Fig. 5), Tricorythidae (Fig. 6), and Heptageniidae.

Heptageniidae body Caenidae dody Tricorythidae body
Group Three - Swimming mayflies. These mayflies are usually streamlined in appearance, their legs are located underneath the body - not splayed out to the side (Fig. 7). Oftentimes when you lay them on their side they have a characteristic curve in the body (Fig. 8). Families include the Baetidae, Isonychidae, and Leptophlebiidae.

Isonychidae body Baetidae body

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