Bats are less difficult to identify than most individuals believe.  The following key has been prepared to aid identification of live individual species found in Idaho and Utah.  Pictures of important species are provided for review.  Important useful characteristics are placed in capital letters where the description of each species has been finalized.  Information to prepare this key has been developed for Utah after Durrant, (1952) and Idaho after Keller, (1985).  Common names are after Jones. et al, (1992).  The following notations and resources were used to provided or expand the information provided in the key:  Head and body, or extremes of total length, forearm measurements are from Hall,(1981).  Tragus lengths are from Durrant, (1952) or were taken from museum specimens.  Weights are from Schwartz and Schwartz, (1981) or museum specimens.  The numerator of numbers above each species indicates the dental formula for one-half of the upper jaw.  The denominator numbers are for one-half of the lower jaw, sequenced as incisors, canines, premolars and molars.  Body size is generalized as total length (tip of the nose to the tip of the tail vertebrae), length of tail (right angle to body from base of the tail to the top of the last vertebrae), hind foot (heel to the tip of the longest toe plus claw), and ear (base of the notch to the margin of the pinna) measured in millimeters and separated by dashes (ie: 135-32-15-8).  Other useful characteristics include the calcar, a cartilaginous spur extending from the ankle region along the margin of the membrane (interfemoral) between the legs.  It is keeled when  tissue occurs on the outside edge of the spur.  The tragus is usually a spike-like piece of tissue projecting up from the base of the ear to the margin.

**= may be resident in Idaho, but no validated specimens collected to 2000.
 
 

1a. Tail projecting CONSPICUOUSLY (more than 10mm) BEYOND INTERFEMORAL MEMBRANE.
           . . . Go to 2

1b. Tail not projecting conspicuously beyond interfemoral membrane.
           . . . Go to 3

2a.  EARS BROAD and SMALL, NOT EXTENDING MARKEDLY BEYOND MUZZLE when laid forward.

1       1 2 3 = 30 OR 32
2-3   1 2 3
Tadarida braziliensis
Brazilian Free-tailed Bat
90-32-9-18
head-body, 46.6-65.2
length of tragus, 6
forearm, 36.6-46.4
weight, 13g

2b.  Ears SQUARISH and LARGE, EXTENDING MARKEDLY BEYOND MUZZLE when laid forward.

1 1 2 3 = 30
2 1 2 3
Tadarida macrotis**
Big free-tailed Bat
141-50-11-27
head-body, 66.6-79.0
length of tragus, 6
forearm, 58.0-63.8

3a.  UPPER SURFACE of INTERFEMORAL MEMBRANE WELL-FURRED to tip of
tail.
           . . . Go to 4

3b.  Upper surface of interfemoral membrane not well-furred to tip of tail.
           . . . Go to 5

4a. Body YELLOWISH to brownish with white-tipped hairs producing a frosted appearance; TAN THROAT PATCH; EARS with BLACK RIMS.

1 1 2 3 =32
3 1 2 3
Lasiurus cinereus
Hoary Bat
124-54-12-16
total length, 134-140
length of tragus, 9
forearm, 46-55
wt., 21-42g

4b.  Upper FUR BUFFY RED with BROWN GRAY-TIPPED hairs producing a frosted appearance; no tan throat patch; ears without black rims.

1 1 2 3 =32
3 1 2 3
Lasiurus blossevillii**
Western Red Bat
103-51-8-10
total length, 91-112
length of tragus 6
forearm, 37.1-43.6
wt., 5-14g

5a.  Ears 19mm (over 3/4 ") or more in length.
           . . . Go to 6

5b.  Ears less than 19mm in length.
           . . . Go to 9

6a.  EARS in LIVING INDIVIDUALS PINKISH, TRANSLUCENT, or in dead individuals, brown and translucent; ears long (37-47mm), and wide; UPPER FUR BLACKISH with PATCHES of WHITE OVER EACH SHOULDER AND at BASE of TAIL; underparts whitish.  Rare.

2 1 2 3 =34
3 1 2 3
Euderma maculatum
Spotted bat
110-50-11-40
total length, 107-115
length of tragus, 17
forearm, 48-51

6b.  Ears not pinkish or translucent brown and less than 37 mm long.
           . . . Go to 7

7a.  GLANDULAR LUMPS on FACE BETWEEN NOSTRILS and EYES; upper fur brownish to grayish-brown, underparts sooty; EARS, brown and MAY be FOLDED or COILED AGAINST BODY WHEN HIBERNATING.

2 1 2 3 = 36
2 1 3 3
Corynorhinus townsendii
Townsend's Big-eared Bat
95-46-9-35
total length, 90-112
length of tragus, 15
forearm, 39.2-47.6
wt., 9-14g

7b.  No glandular lumps on face between nostrils and eyes
           . . . Go to 8

8a.  UPPER FUR YELLOWISH to PALE-CREAMISH BROWNISH, underparts buffy to buffy white; EARS UP TO 15mm ACROSS AT WIDEST POINT; tragus less than 1/2 the length of ear.

1 1 1 3 = 28
2 1 2 3
Antrozous pallidus
Pallid Bat
110-43-11-31
total length, 92-135
length of tragus, 16
forearm, 48.0-60.2
wt., 14-28g

8b.  Upper fur brownish, dark at base, underparts buffy; BLACK EARS 9-10mm ACROSS at WIDEST POINT; TRAGUS MORE THAN 1/2    LENGTH of EAR.

2 1 3 3 = 38
3 1 3 3
Mytois evotis
Long-eared Myotis
88-41-8-20
head-body, 41.6-56.0
length of tragus, 9
forearm, 35.5-41.0
wt., 5g

9a.  TIP of TAIL EXTENDS UP TO 4mm BEYOND INTERFEMORAL MEMBRANE; upper fur chocolate brown or reddish-brown, underparts paler; size relatively large, forearm usually more than 45mm; wing span may exceed 32cm.

2 1 1 3 = 32
3 1 2 3
Eptesicus fuscus
Big Brown Bat
115-46-12-14
total length, 87-138
length of tragus, 9
forearm, 39-53.6
wt., 14-21g

9b.  Tip of tail does not extend much beyond interfemoral membrane; color variable; forearm less than 45mm.
           . . . Go to 10

10a. Color of upper fur variable, but neither smoky gray nor blackish to brownish, with some silver-tipped hairs.
           . . . Go to 12

10b. Color of upper fur either blackish or brownish with some silver-tipped hairs or bat small and upper fur pale buff to pale smoky gray.
           . . . Go to 11

11a. Upper interfemoral membrane heavily furred outward from body for slightly more than 1/2 of its length; BODY VERY DARK BROWN OR BLACKISH WITH SILVERY-WHITE TIPS TO THE HAIRS GIVING A FROSTED APPEARANCE.

2 1 2 3 = 36
3 1 3 3
Lasionycteris noctivagans
Silver-haired Bat
93-39-8-6
total length, 92-115
length of tragus, 8
forearm,
wt., 8-11g

11b. UPPER INTERFEMORAL MEMBRANE SPARSELY FURRED OUTWARD FROM BODY FOR ABOUT 1/3rd OF LENGTH; wing membrane and ears blackish, upper fur pale buffy brown to PALE SMOKY GRAY, fur distinctly darker at base; A SMALL BAT; TRAGUS BLUNT, END BENT FORWARD; EARS FURRED ON UPPER SIDE ADJACENT TO BODY; interfemoral membranes blackish.

2 1 2 3 = 34
3 1 2 3
Pipistrellus hesperus
Western Pipistrelle
70-26-6-11
total length, 60-86
length of tragus, 4
forearm, 29-31

12a.  FRINGE OF STIFF HAIRS ALONG FREE EDGE OF INTERFEMORAL MEMBRANE, ESPECIALLY NEAR TAIL; ears, laid forward, extend 5mm or less beyond nose.

2 1 3 3 = 38
3 1 3 3
Myotis thysanodes
Fringed Myotis
85-37-8-17
head-body, 43-52
length of tragus,
forearm, 39.8-46.0

12b.  No fringe of stiff hairs along free edge of interfemoral membrane; ears laid forward reach nose or only very slightly beyond.
           . . . Go to 13

13a.  FUR ON UNDERSIDE OF WING MEMBRANE EXTENDING FROM THE BODY TO A LINE JOINING THE ELBOW AND KNEE; body cinnamon to brownish above and buffy to light brown below; membranes and short rounded ears dark.

2 1 3 3 = 38
3 1 3 3
Myotis volans
Long-legged Myotis
91-42-11-14
head-body, 43-54
length of tragus, 5
forearm, 35.2-41.2
calcar keeled

13b. Fur on underside of wing membrane not extending from the body to a line joining the elbow and knee.
           . . . Go to 14

14a.  Distinct black mask across muzzle and face to ears; ears blackish; upper fur color variable brown with ORANGE TONE.

2 1 3 3 =38
3 1 3 3
Myotis cilliolabrum
Western small-footed Myotis
79-36-7-13
head-body, 34.4-4
forearm, 29.6-36.0
calcar keeled

14b.  No distinct mask across muzzle and face to ears; ears blackish or brownish; upper fur color variable brown.
           . . . Go to 15

15a.  TIPS of HAIRS IMPARTING INCONSPICUOUS BRONZE TONE, especially when fur ruffled; yellowish to olive-brown fur on back appears long and glossy; calcar not keeled.

2 1 3 3 =38
3 1 3 3
Myotis lucifugus
Little Brown Myotis
85-36-11-13
head-body, 41-54
length of tragus, 8
forearm, 33.0-41.0
wt., 7-9g
calcar not keeled

15b.  Tips of hairs not imparting inconspicuous bronze tone; color variable, but dull.
           . . . Go to 16

16a.  Interfemoral membrane, above and below, with hair extending to slightly beyond a line joining the knees;  CALCAR NOT KEELED; upper fur and interfemoral membranes PALE BROWN; FOOT RELATIVELY LARGE, 9-10mm.

2 1 3 3 =38
3 1 3 3
Myotis yumanensis
Yuma Myotis
85-36-11-13
head-body, 37.8-49.0
length of tragus,
forearm, 32.0-38.0

16b.  Interfemoral membrane, above and below, with hair not extending to slightly beyond a line joining the knees; CALCAR KEELED; fur yellowish chestnut or brown above, paler below; FOOT RELATIVELY SMALL, 6-7mm.

2 1 3 3 =38
3 1 3 3
Myotis californicus
California Myotis
82-38-6-11
head-body, 35.0-44.8
length of tragus,
forearm, 29.0-36.2