How to Tell if a Darkling Beetle is Male or Female: Easy Identification Tips

Darkling beetles are fascinating insects, but determining their gender can be a bit tricky. These nocturnal scavengers come in various sizes and forms, usually presenting a dark or brown coloration. Before we dive into identifying the gender differences, let’s get a clearer understanding of these beetles that are found in diverse habitats like woodlands, deserts, and agricultural fields.

Understanding the key differences between male and female darkling beetles may pique the interest of hobbyists and researchers alike. While visible differences may be subtle, they do exist, and familiarizing yourself with the features of each gender can be helpful in the long run, especially for those who have a keen interest in studying or breeding these fascinating insects.

Darkling Beetle Basics

Darkling beetles are part of a large family of insects within the arthropods. They are often found in various environments, scavenging on the ground for food. The most common species, Tenebrio molitor, is known for its dull black or brown appearance and smooth abdomen.

Darkling beetles display sexual dimorphism, making it possible to distinguish males and females. However, this difference is subtle and may require some practice to recognize. Males typically have longer, thicker antennae, while females have shorter, finer ones.

Examples of identifying features for darkling beetles include:

• Dull black or brown color
• Scavenger behavior
• Smooth or textured abdomen

Here is a comparison table to help distinguish between male and female darkling beetles:

While observing these insects, keep in mind that practice makes perfect. As you become more familiar with darkling beetles and their unique characteristics, you’ll improve your ability to tell males and females apart. Remember to always handle them gently and respectfully to ensure their well-being.

Sexing Live Adults

Size and Swelling

Darkling beetles have distinct differences in size and swelling between males and females. To identify them:

• Male darkling beetles are generally smaller in size compared to females.
• Female darkling beetles have a swollen abdomen, especially during mating season or when carrying eggs.

Ventral Side Examination

A more accurate way to determine the sex of darkling beetles is by examining their ventral side. Key differences include:

• Males have a more rounded tip on the last abdominal segment.
• Females possess a more pointed tip on the last abdominal segment.

Here’s a comparison table for easy reference:

Remember, when sexing live adults, handle them gently and with care to avoid causing any harm.

Morphological Characteristics

Tail and Chase

Darkling beetles display differences in their tails as a way to distinguish males from females. Males often have curved or longer tails, while females have shorter and straighter tails. Here’s a comparison of the two:

One example is the Darkling Beetle species, where males typically have elongated and curved tails.

Microscopic Examination

Another way to identify a male or female darkling beetle is through a microscope. By examining their reproductive organs, it’s possible to determine their sex.

• Males have a pair of genitalia called parameres.
• Females have a tubular structure called spermathecae.

Studying these structures under a microscope can make sexing darkling beetles more accurate, though it may be a more painstaking task when compared to observing tail characteristics.

Reproduction and Lifecycle

Mating Behavior

Darkling beetles reproduce sexually through a process where the male locates and courts the female. The male quickly strokes his antennae and front pair of legs to attract the female during mating (source).

Eggs and Larvae

• Female beetles lay eggs that hatch in 7-10 days (source).
• Newly hatched larvae are called mealworms.

Darkling beetles go through a complete metamorphosis with four different body forms. The first form is the egg, and then the beetle hatches into a larval form called a mealworm. As mealworms mature, they transition into the pupal stage before becoming adult darkling beetles. Here’s a comparison of the egg and larval stages:

In conclusion, you can identify darkling beetles’ sex by observing their mating behavior, and the lifecycle involves eggs hatching into mealworms and eventually transitioning to adult beetles.

Ecological Impact and Research

Bioindicator in Environmental Pollution

Darkling beetles can serve as useful bioindicators in monitoring environmental pollution. Some reasons include:

• Their abundance in various habitats
• Sensitivity to changes in environmental conditions

For example, changes in darkling beetle population size or behavior might indicate the presence of pollutants in an ecosystem.

Influence of Chemical Insecticides on Mortality

Chemical insecticides can have a significant impact on darkling beetle mortality rates. Here’s a comparison of two commonly used insecticides:

While both insecticides are used to control pests, Insecticide A has a more substantial negative impact on darkling beetle populations than Insecticide B. It is essential to consider the ecological impacts when selecting and applying insecticides.

Additional Darkling Beetle Species

Pimelia Senegalensis

Pimelia Senegalensis is a species of darkling beetles belonging to the Tenebrionidae family. Physiological studies on this species have been conducted to gain insights into their growth and development:

• They primarily feed on boiled spaghetti and rice for research purposes
• Genitalia examination helps in determining their gender

Some external morphological characteristics of Pimelia Senegalensis include:

• Variety of colors, usually dark
• Distinct patterns on their back (elytra)

Pimelia Angulata

Pimelia Angulata is another species of darkling beetles, having unique features:

• Found mostly in arid and semi-arid regions
• Active during the night, hiding from predators during the day

Pimelia Angulata is related to the Pimelia Senegalensis, but it bears differences in its external appearance:

Pterolosia Squalida

Lastly, Pterolosia Squalida is a species involved in locust control operations in agriculture, as they feed on locust eggs:

• Predatory nature helps in managing locust populations
• Part of the Tenebrionidae family of beetles

Some characteristics to note about Pterolosia Squalida are:

• Generally smaller compared to other darkling beetles
• Grayish-brown in color

In summary, Pimelia Senegalensis, Pimelia Angulata, and Pterolosia Squalida are three darkling beetle species, each having unique features and roles within their ecosystems.

Reader Emails

Over the years, our website, whatsthatbug.com has received hundreds of letters and some interesting images asking us about these insects. Scroll down to have a look at some of them.

Letter 1 – Darkling Beetles: Edrotes ventricosus

Identification request
Location: Moapa, Nevada
January 28, 2012 8:43 pm
I’m after an identification confirmation or other options. Images of Paracotalpa deserta are the hardest to find of the four species. That said, this matches Field Guide to Beetles of California description for a ”Little Bear” scarab beetle with January thru March time of appearance, creosote-bursage desert habitat, and general description as ”black”. These were 9mm long.
Signature: Bruce Lund

Dear Bruce,
The antennae on these beetles are wrong for a Scarab.  We believe we have correctly identified it as a Darkling Beetle, Edrotes ventricosus, by matching to photos posted to BugGuide.  The species has been reported in California and Nevada.

THANK YOU for the identification AND especially for the antennae comment.
The latter sent me back to field guides and websites to look at what I
missed and OF COURSE the antennae are not correct for a scarab beetle and
are correct for the Tenebrionidae. I’m just starting to work in the
insects and my learing curve is nearly vertical.
Bruce

You are most welcome Bruce.  It always helps to have more than one set of eyes when doing unusual or difficult identifications.

Letter 2 – Darkling Beetles from the Philippines

Subject: Darkling beetle
Location: Miagao Iloilo, Philippines
July 30, 2012 2:35 am
Good day Sir Daniel
I have collected this darkling beetle from a Rain Tree- Samanea saman, in the Philippines, Miagao Iloilo last July 15, 2012.Months of July here in the Philippines is a rainy season. I think this is from the family tenebrionidae, I have observed that when I disturb them, they will cluster back again under the bark that i have collected, they are somewhat afraid of light or something, the size is 3mm-8mm long can you identify the scientific name or even in genus level of this beetle pleasee it will be a very big help
Thanks!
Signature: Ed

Hi Ed,
We agree that this appears to be a Darkling Beetle, but we are unable to provide any species or genus information.  The easiest species to learn about on the internet are large and conspicuous creatures or dangerous or harmful creatures.  Relatively nondescript species like this beetle will pose a tremendous challenge to properly identify.

Letter 3 – Darkling Beetle from the Canary Islands

Small beetle on Lanzarote
February 14, 2010
Hello,
in our holidays we found on Lanzarote a beetle which is lighter blue with black stripes. It may be about one cm long (unfortunately I didn’t measure it). This specimen crawled not far away from the coast on the ground between the lava stones (harbour region of Arrecife).
I would be pleased, if you could tell me, which species it is.
Greetings, Heidrun Terasa
Near Arrecife, Lanzarote, Canary Islands

Dear Heidrun,
Our initial attempts to identify your beetle have proven fruitless.  We are posting the image and we hope one of our readers will be able to assist in its identification.

Karl figures it out
I can’t be certain but I think this a Darkling Beetle (Tenebrionidae) in the genus Pimelia. There are approximately a dozen species in the Canary Islands. Most or all of them are endemic and many occur on only a few or even one island. The only species that occurs on Lanzarote is P. lutaria. I could find no online photos, but P. lutaria is described as being covered with short ash colored hairs, which give it a “muddy” appearance. Perhaps this could also appear blueish under certain light conditions. Apparently many of the Pimelia species on the islands are considered to be under threat or even endangered, but P. lutaria is still abundant throughout Lanzarote. If you care to download a pdf file (in Spanish) the second link below takes you to a fact sheet for P. fernandezlopezi, a very similar looking beetle that occurs only on the island of La Gomera. Regards.
http://www.gobiernodecanarias.org/cmayot/medioambiente/centrodocumentacion/publicaciones/revista/2000/19/250/
http://carn.ua.es/CIBIO/es/lrie/fichas/Pimelia%20fernandezlopezi.pdf

Letter 4 – Drowned Darkling Beetles from Dubai: Tok-Tokkies

Can you identify this please?
Location: Dubai
November 29, 2010 8:48 am
Hi there, i live in Dubai and found these 2 little fellow’s floating in the pool this morning. Well, i say little, they were actually quite big as you can see from the pitures. And very black! Ive never seen beetles that big before so i fished them out and too pictures. Any idea as to what kind they are? Thanks.
Signature: Dee

Dear Dee,
We believe your beetles are Darkling Beetles in the family Tenebrionidae.  Though it only covers North American species, you may read more about Darkling Beetles on BugGuide.  Swimming Pools are notorious death traps for insects and other small creatures that forage about at night.

Letter 5 – Darkling Beetle: Coelocnemis californica

Big Black Beetle
As a young boy I was quite the bug collector: everything I ever caught I would study religiously until I knew the creature inside and out. At the tender age of 10, I considered myself an expert in the field of Centipedes and Earwigs. One insect I occasionally came across in my little bug hunting adventures as a kid was what I labeled the ”Big Black Beetle”. I become quite fascinated with the beetle and wanted to know more, but my search to find more answers about the bug proved to be unsuccessful. And as time went on I, unfortunately, stopped looking for bugs all together as other hobbies and interests beckoned, and the mystery of the ”Big Black Beetle” seemed to be forgotten. Then last week at work (I work at a log home construction site) I found it! I was lifting up some boards and spotted the little guy. Maybe you guys can help me solve this mystery once and for all!
Thanks,
Braden

Hi Braden,
We are fairly certain this is a Darkling Beetle, possibly in the genus Eleodes, but we want to check with Eric Eaton for substantiation and perhaps a species identification. A location would be a tremendous help. Eric wrote: ” LOOKS like an Eleodes, but not knowing where exactly it was collected, I won’t say for certain. Other genera of Tenebrionidae can look nearly identical. Eleodes are typical of true deserts. Coelocnemis and Iphtheminus (spelling?) tend to replace Eleodes at higher elevations, like in Ponderosa pine forest habitats.”

Thanks for your help guys! I live in British Columbia, Canada. For some reason I thought I included my location in my initial e-mail, sorry about that!

Update:  June 18, 2021
That probably is Coelocnemis californica in the photo. There is a great deal of mimicry between Coelocnemis and Eleodes, and in some areas they are quite difficult to tell apart from a distance. The surest way to differentiate Coelocnemis from Eleodes is to look at the ventral edge of the tibiae; Coelocnemis has a double row of golden setae which is completely absent from Eleodes.
C. californica is known from British Columbia and as far east as Montana. Its conceivable that it ranges further north and east, and its also possible that it has been spread by the human movement of firewood and other things as several other large tenebs have been.
Hope that helps you.
John Nelson

Letter 6 – Darkling Beetle: But Which Species???

Subject: Philolithus morbillosus?
Location: West Texas
April 29, 2013 12:02 pm
We took this picture in Guadulupe Mountians National Park in West Texas. The only think I found similar to it on the internet is Philolithus morbillosus. We found it in July of 2012.
Signature: Tinker

Dear Tinker,
We do not believe you have correctly identified this Darkling Beetle correctly.  If you look at the images of Philolithus morbillosus from BugGuide, you can see that the elytra or wing covers are more sculpted and the shape of the thorax is different.  We also believe you have the correct tribe, Asidini, as well as the correct family Tenebrionidae, the Darkling Beetles.  See examples of Asidini on BugGuide.  We will try to get Eric Eaton’s opinion, however he informed us he is traveling and will have limited internet access.

Eric Eaton confirms our suspicions
Daniel:
No, we are traveling NEXT week.  I’ve got blog assignments for a third party, though, so….
I believe this is a species of Asidopsis, but there are other similar genera, so….
Eric

Thanks Eric,
We suspected this was in the tribe Asidini, and Asidopsis seemed like a good possibility.

Letter 7 – Darkling Beetles

Subject:  Teneb captives
Geographic location of the bug:  CA
Date: 01/25/2018
Time: 02:10 PM EDT
Your letter to the bugman:  Ah, the power of food! Insects lose much fear of man in this state.
The shinier teneb is Coniontis, and despite being only 10 mm long it has been alive since summer, when I rescued it. I am currently trying to record its mysterious vibratory song, which has never been done before.
The duller one did not come from the local area, and identity is unknown.
PS: I’ve attached a bonus pic of the pet Cotinis dozing on top of its meal
How you want your letter signed:  AlexW, extreme entomophile

Dear Alex,
Thanks for sending us an image of your captive Darkling Beetles.  Eric Eaton once told us that if we are ever having trouble identifying a Beetle, it is most likely a Darkling Beetle.  Good luck with the sound recording.  The song to which you refer is a result of stridulation, or producing sound by rubbing body parts together, which no doubt you already know, but we write it for the benefit of our readership.

Hello Daniel, I have one more minor nit to pick. I forgot to include that the Coniontis’s song consists of a short spurt of vibrating the body against substrate, and thus “stridulation” may not be the right term. I affectionately call my Coniontis the “tok-tok of Los Angeles” for this reason =)

Letter 8 – Orgiastic Darkling Beetles

Subject: ground beetles
Location: Anza, California
September 18, 2012 8:38 pm
Thought you might want to put this up on the Bug Love board, sorry it’s not focused better.
Love this site!
Signature: Mary Ann

Dear Mary Ann,
We are aghast at this photograph.  We cannot imagine what prompted so much sexual activity in such a confined space.  These are not Ground Beetles.  They are Darkling Beetles.  We are nearly certain they are Desert Stink Beetles or Acrobat Beetles in the genus Eleodes, which you can verify on BugGuide.  They will stand on their heads, stick their rear ends in the air and release a malodorous smell if disturbed, hence the common names.  We will check with Eric Eaton for confirmation on that identification.  Your photo is both an amazing documentation of natural history as well as a humorous amusement.  We are going to feature it on our homepage banner.

Thank you, that explains a lot.  They act like stink beetles, but I’ve never been able elicit an odor from them (I’ve heard if you squash them you can smell them, but I cant’ bring myself to do it).  I have a theory on the sex, the females are eating and are blocked from going forward, and the males seized the opportunity. <gg>  I am very flattered that the photo is on the homepage banner!!

Eric Eaton makes a correction
Hi, Daniel:
Those look to me to be darkling beetles in the genus Coelocnemis rather than Eleodes.  Coelocnemis tends to like dry forest habitats.  Here’s more:
http://bugguide.net/node/view/50466
Thanks for sharing.  I suspect the females are gathered at oozing sap and the males are taking advantage 🙂
Eric

Letter 9 – Pie Dish Beetle is no longer Unknown Australian Darkling Beetle

can’t rest until I know
It’s Christmas Day ’06… Merry Christmas! I live close to Perth in Western Australia and I have always had a fascination with all manner of bugs, but today I came across one that really caught my attention and I have never come across in all my almost 44 years on this amazing Earth! I have this problem where I can’t rest until I know what a thing is that captures my interest so and this is why I am sending these photos to see if you can help me? I checked out your wonderful beetle pic collection, but did not see it there. If you can tell what sex it is I’d also be interested in that, but mainly just what it is called. I know you’re busy.. but it’s your own fault for having such a great site. Thanks in advance,
Jill

Hi Jill,
We have been researching on the internet for the past hour and have nothing conclusive for you. Our first inclination, really just a guess, is that this is some species of Carrion Beetle in the family Silphidae. A google search lead us to an image of Ptomaphila perlata that is somewhat similar, but definitely not a species match. We are calling in the big guns with Eric Eaton to see if he at least agrees with the general identification of a Carrion Beetle. Each image we opened was more interesting than the last, so we are posting three in the hopes that some reader can give both you and us a conclusive identification as we will have trouble resting as well. Here is what Eric Eaton believes: “I’m pretty sure this is a darkling beetle in the family Tenebrionidae. It resembles our American genus Embaphion, in fact. Eric”

(12/27/2006)
I can rest because now I know It’s a type of pie dish beetle! Thank you for your time… I should have mentioned that the bug in question was about an inch long by half an inch wide… quite large really!
Jill

Ed. Note:  Pie Dish Beetle
January 30, 2010
We are doing some housecleaning and recategorizing some of our archive entries, and we found a broken link which we fixed.  The Pie Dish Beetle is Pterohelaeus cornutus or Pterohelaeus piceus.  The species is also known as a False Wireworm.

Correction: January 11, 2011
In researching a new posting today, we believe we have identified this Hairy Backed Pie Dish Beetle as Helea perforata on FlickR.

Letter 10 – Darkling Beetle: Eusattus difficilis

Subject: ID a beetle
Location: Southcentral California, desert
March 12, 2013 11:34 am
bugman: I was recently in Joshua Tree National park and saw two different beetles. One was clearly the Pinacate or Darkling (also called stink bug, clown beetle), but the other one, shown below I could not identify.
It was about the size of my little finger’s nail, so about 3/8of an inch or so across, black and round-backed. As you can see from the photo, it does not have a protruding head. We were in the western (Mojave Desert) portion of the park. It was a fast running bug.
Any help in identifying it would be appreciated.
Alan
Signature: Alan Palisoul

Hi Alan,
Eric Eaton, who has been a tremendous help to us through the years, advised us long ago that if we couldn’t identify a beetle, chances were good it was a Darkling Beetle, so that is where we looked.  We believe we may have identified your beetle as a member of the genus Eusattus, based on this photo of Eusattus reticulatus posted to BugGuide.  We will contact Eric to see if he can confirm or correct our identification.

Eric Eaton Responds
Hi, Daniel:
Definitely a species of Eusattus, but I am by no means an expert on Tenebrionidae.  I’m not even sure who the contemporary experts are these days.  Triplehorn is still alive, and very courteous and helpful, but I hate to bother him.  He deserves a peaceful retirement 🙂
Eric

Daniel:  Thanks so much for getting back to me and doing so this quickly. IOn this same trip I got a couple of nice shots of a Darkling, one with it standing on it’s head. That was fun.
Thanks again, look forward to any more information you get.
Alan

Letter 11 – Darkling Beetle Larva, NOT Leatherjacket!!!

Subject:  Mystery bug
Geographic location of the bug:  Ohio
Date: 03/31/2019
Time: 12:42 PM EDT
Your letter to the bugman:  I’ve never seen anything like this. Found on the floor of my house.
How you want your letter signed:  Matt

Dear Matt,
This appears to be an immature Fly, possibly a Leatherjacket, the larva of a Crane Fly.

Ed. Note:  We received a comment that this is a Darkling Beetle larva.  Here is a somewhat similar looking image from FLickR.

Letter 12 – Roughened Darkling Beetle

Coelocnemis
Location: Western Maine, USA
May 11, 2011 6:15 pm
I found this black beetle in my wood pile. We live in Western Maine if that narrows it down. Aprox. 1.5cm.
Signature: Thank you for considering, Castor Knox

Dear Castor,
It required considerable searching before we finally identified your beetle as a Roughened Darkling Beetle, Upis ceramboides, by matching the photo to postings on BugGuide.  You were on the right track with your theory that it might be in the genus Coelocnemis, because that is also classified as a Darkling Beetle in the family Tenebrionidae.

Letter 13 – Leaf Beetle from France

Subject: Black Beetle
Location: Gard, France
November 2, 2014 3:31 am
Hello!
Could you tell me what kind of beetle this is? I frequently see them wandering around the garden – when picked up, they grab onto your finger and then cover it in some kind of weird red liquid.
I assume they’re trying to pretend they bit you?
Either way, as such a frequent visitor, it’s a bit annoying not knowing their name!
Signature: Kinyonga

Dear Kinyonga,
The best we are able to provide at this time is a family name.  This is a Darkling Beetle in the family Tenebrionidae.  We did a quick search but could not find any matching images with identifications.  Perhaps one of our readers will have better luck with a species name.

Ed. Note:  Thanks to a comment from beetlehunter, we now know that this is actually a Leaf Beetle, Timarcha tenebricosa, which is well represented in online images including these images on Nature Spot and Panoramio.  Nature Spot indicates the common name Bloody-Nose Beetle and states:  “It earns its common name from its peculiar form of defence; when threatened it exudes a drop of bright red fluid from the mouth. The larvae are a metallic bluish colour.”  That is illustrated on Fotonatura.  It is very interesting that the species name in the binomial shares the same root as the family name Tenebrionidae, so the resemblance Darkling Beetles was noted by Fabricius when he named the beetle in 1775. 

Reader Emails

Over the years, our website, whatsthatbug.com has received hundreds of letters and some interesting images asking us about these insects. Scroll down to have a look at some of them.

Letter 1 – Pie Dish Beetle from Australia

Subject: Strange looking bug
Location: Perth, Western Australia
December 2, 2012 10:18 am
I must say, I’ve never seen anything like this one before. I quickly ran in to grab my phone and snap up some of these pictures. At first it wasn’t moving and I thought it was just something that had fallen off a tree, but then it decided to run! I’ve been looking everywhere for something like this and have absolutely no idea.
Signature: David, Perth, Australia

Hi David,
We love the common name of this Pie Dish Beetle, one of the Darkling Beetles in the family Tenebrionidae.  The Brisbane Insect website identifies three species of Pie Dish Beetles in the genus Pterohelaeus, but they do not state how to distinguish them from one another.