Maccaffertium modestum/mediopunctatum
Maccaffertium modestum
Nymph 3
Body: Flat head and body. Head as wide as body. Dorsal: amber to medium-brown, variously marked or mottled. Ventral: Pale-yellow to yellow with small black spots or chevron-type banding on the underside of several abdomen segments.
Tails: Three tails, side tails are held out widely.
Nymph Look Alikes 4
Nymph Look Alikes: Maccaffertium modestum and M. mediopunctatum nymphs look a lot like the many other Maccaffertium species nymphs, and trout streams typically support at least two or three such species. As such, field identification of the nymphs to species is very difficult. Among the flat-bodied mayflies, only Maccaffertium nymphs exhibit the chevron-shaped bars on the underside of the abdomen, allowing for field identification of the nymphs to genus. However, a number of species share this character (M. mediopunctatum, M. Ithaca, and the less-common variant form of M. modestum in NE, precluding species-level field ID), and when it’s lacking, field identification even to genus can be difficult.
DUN (SUBIMAGO) 3
Size: 9-12 mm.Body: light cream to pale greenish yellow with a lighter underbody.
Wings: Pale cream to light yellow-grey, with hazy brown cross veins and patchy mottling.
Tails: Two tails (nymphs have three).
SPINNER (IMAGO) 3
Size: 10-12mm.
Body: Pale yellow to pale ochre and creamy/white abdomen.
Wings: Hyaline (clear) wings.
Tails: Two tails.
Dun/Spinner Look Alikes 4
Dun/Spinner Look Alikes: The creamy white abdomen of these medium-sized mayflies render them not easily confused with other mid-to-late-summer mayflies. As duns, only the other Heptageniidae will potentially be mistaken for these Cream Cahills, but among the Heptageniidae duns with marked or mottled wings, only Maccaffertium, Stenonema, and Stenacron species have a dark band on the femur. This combination of characters will rule out most other genera. The Stenacron species (Light Cahills) can be distinguished from Maccaffertium by the presence of a small patch of black color on the forewing that extends between 2 or 3 crossveins. Stenonema femoratum is also known as the Cream Cahill, and separating this genus from the Maccaffertium species of interest will require the aid of magnification and a species key. Central New England anglers may also encounter Stenonena Ithaca, also known as
the Light Cahill. While this hatch is said to occur earlier in the season than those of the Cream Cahills, all life stages are strikingly similar to those of the Cream Cahills, with sometimes only subtle differences in coloration. Whenever a “Cahill” hatch is encountered, collection of specimens for later examination under magnification will best ensure accurate identification.
Spinners of the Maccaffertium sp. Cahills can also be confused with those of Epeorus vitreus, another Heptageniidae mayfly that hatches in late summer. While the male spinners are strikingly similar in size and coloration, the two genera can be distinguished by the positioning of the eyes. Eyes of the male Epeorus are touching or very nearly, while those of Maccaffertium are separated by a distance equal to or greater than 1⁄4 the width of an eye. Note that eye color is not a distinguishing characteristic between these two genera, as eye color can change with exposure to light.
Habitat & Distribution 3
The Maccaffertium species group is represented by at least eight species in central New
England, and at least three of these species – M. modestum, M. mediopunctatum, and
M. mexicanum integrum are colloquially known as Cream Cahills. Other Maccaffertium
species are known as the March Brown (M. vicarium) and Light Cahills (such as M.
Ithaca, M. terminatum). Nymphs prefer the moderate-to-fast water of swift runs and
riffles, where they crawl about gravels and cobbles.
Life Cycle - Emergence 3
Maccaffertium sp. nymphs are generally known to crawl into the shallow, slower stream
margins about a week before emergence, but late-summer hatches may occur in mid-
channel. Emergence typically occurs in the mid to latter parts of the day, warmer
weather inducing later hatches. Spinners return to the river days after hatching for
mating and egg laying. Spinners gather over the water in the evening and can be seen
over the stream into darkness; spinners fall spent to the water after dark, but not
typically in large numbers.
Massachusetts:Maccaffertium modestum is reported as an earlier hatch (approximately
June into August) than M. mediopunctatum (July into September, potentially later on
some waters), but both of these ranges are approximations.
Degree of Difficulty 3
This table is meant to help users get an idea of how easy/hard it is to ID this species to any taxonomic level, and to give an idea of the characters (or features) that are important to accurately identifying a specimen. As a general guideline, these degree of difficulty levels translate to the type of effort needed to reliably ID a specimen to that taxonomic level, as long as the associated features are confirmed. Of coarse there will/may be exceptions to these general rules.
Maccaffertium modestum/mediopuncatum
Taxonomoic level
Taxonomic Name
Feature
Degree of difficulty
Order
Ephemeroptera
Wing Shape
1
Family
Heptageniidae
2 tails
2.5
Genus
Maccaffertium
9-12 mm, could be confused with late season sulphers, and can be confused with voterus, can tell apart by looking at eyes
4
Species
modestum
July-August
NA
Species
mediopunctatum
July-September
NA
Degree of Difficulty
Degree of Difficulty
Description
1
Can be ID’d on the wing or water.
2
A specimen in the hand can be ID’d.
3
Can be ID’d by studying a decent photo of the specimen.
4
Can be ID’d by studying a captured & preserved specimen, usually under some magnification.
5
Proper ID requires study of preserved specimen under magnification, usually looking for some feature that can be difficult to confirm. Usually requires training or confirmation from a professional.
Sources and Credits
- (c) Jeff Webb, some rights reserved (CC BY-NC-SA), https://www.flickr.com/photos/22295793@N07/7203283120/
- (c) Bob Henricks, some rights reserved (CC BY-SA), https://www.flickr.com/photos/aquaticinsects_of_central_virginia/14418059372/
- (c) Jay Aylward, some rights reserved (CC BY-SA)
- Adapted by Jerry Schoen from a work by (c) Jay Aylward, some rights reserved (CC BY-SA)
