Hornworms and Calcium, the truth

What are the best methods to deliver Calcium to your reptiles?  Proper calcium is critical to the health of your pet reptile’s bones – especially rapidly growing reptiles – but it’s not as simple to supplement as you might think.

Timberline is a live food producer for pet stores, zoos, breeders and hobbyists.  We place a strong focus on nutrition and science providing fresh food that matches what an animal would eat in the wild.  Our commitment to natural, high quality nutrition is proven by our nutritionally superior, patented product line called Vita-Bugs.  Vita-Bugs are the perfect solution for all reptile dietary needs that are reflected in the bugs reptiles would naturally eat in the wild.  But even our patented product line can’t deliver the proper amount of calcium (Ca) that most captive reptiles need to avoid painfully debilitating nutritional deficiencies.

It’s important to note here, at the beginning of this post, that we’ve been asked if hornworms are a viable option to deliver calcium to your reptiles.  The answer to that question is unequivocally NO!  Hornworms cannot possibly deliver satisfactory calcium levels to your reptile, even if you feed hornworms EXCLUSIVELY.  We’ve been disappointed to find several websites that claim the contrary.  Many of these websites publish accurate calcium mg/kg values, but claim them to be significant.  At best, it’s a misunderstanding and at worst it’s deception – both of which will damage the health of many pet reptiles.  We will set the record straight here in this article.

This blog post is designed to be a thorough explanation of calcium, it’s importance to reptile health, and how it needs to be delivered to be effective.  We will also address misinformation about the calcium content of common feeder insects to help save the health and lives of many pet reptiles across our hobby.

There are three ways to deliver calcium to your pet reptiles – Dusting, Gut-loading, and by feeding insects that are naturally sufficient.  Before we dive into what the pitfalls of calcium supplementation are, let’s dive into a short, concise science lesson.

Most commercially raised feeder insects such as crickets, mealworms, waxworms, superworms, roaches, fruit flies and hornworms have very little use for calcium in their bodies.  They don’t have any bones or teeth that require significant levels, so even when they consume calcium rich foods, they pass that calcium right through their bodies - never accumulating it.  Technically speaking, most commercially raised feeder insects will never be a sufficient calcium source by themselves – with one exception, the Black Soldier Fly Larvae.  We’ll get back to black soldier fly larvae shortly.

For calcium to be effectively utilized by your pet, it must be paired with a mineral called phosphorus (P).  For each calcium molecule to be useable, it must be paired with a molecule of phosphorus.  Phosphorus is abundant in most feeder insects – therefor in your reptile, so the delivery of Calcium to pair with the phosphorus already in your reptile’s system should be your goal.

Let’s walk through the methods for dusting and gut-loading while shining a light on the pit-falls and misguided information surrounding these methods.  It will be obvious why we often refer to dusting and gut-loading as an exercise in “hocus-pocus”.


Dusting is fairly self-evident.  By simply coating feeder insects with a high-quality calcium powder and feeding them directly to your pet you’re accomplishing the calcium delivery in a method you can observe. 

There are a few problems with dusting that we’d like to make clear.  First, there is no way to measure the amount of calcium you’re delivering to your reptile.  Calcium sticks very well to some feeders, and poorly to others.  Some bugs groom themselves rapidly, and some don’t.


Gut-loading is a method of feeding insects a diet packed with nutrients including calcium, to “load” up the bug with a belly full of nutrients to then feed directly to the reptile.  Those who know recommend that insects are gut-loaded for 24 to 48 hours to ensure proper loading. 

Again, the discerning observer will be able to identify a few concerns.  First, a diet rich in calcium will eventually poison most feeder insects in a short period.  Second, many of the commercially available gut-loads make disappointingly deceptive statements about the product’s actual contents, and its ability to deliver the nutrients promised on the label to an insect.  Third, insects make it a frequent habit of expelling their belly contents.  For anyone who has spent much time with crickets, they poop – a lot – expelling all that valuable nutrition that is never delivered to the reptile.

Dusting and gut-loading can, and have often been, tried and true methods to deliver proper calcium to reptiles.  Unfortunately, poor products, poor practices and inconsistent results leads us to call the practices “hocus pocus”.  Not only are the methods of dusting and gut-loading unreliable, but our research shows that hobbyists don’t always get around to dusting or gut-loading at all.

We prefer to be sure that we are delivering high quality calcium in a natural format and the proper levels.  We strongly recommend supplementing reptiles’ diets by making 15% of the reptiles’ total bug diet Calciworms (Black Soldier Fly Larvae).  Calciworms are naturally high in calcium – containing 19X the calcium levels of crickets with a perfect ratio of Ca:P of 3:1. 

Calciworms are a unique insect that has developed a calcified exoskeleton which demands accumulation of calcium into the bug itself.  Calciworms are found spread liberally around the entire globe and may be a consistent source of calcium to reptiles in the wild.  There are also another group of about a dozen insects that we know of in nature that could also be good natural sources of calcium for reptiles in the wild.  At this time, none of those other high-calcium bugs are produced commercially.

Where do common feeder insects stack up when it comes to Calcium?  Let’s look at the numbers.  It is recommended that calcium should be present in a concentration of 5,000 (mg/kg dry wt) to be considered a viable calcium solution for reptiles.  As you can see, hornworms are less than ½ of that recommendation and wholly inadequate.  As a matter of fact, no commercially raised feeder insect should ever be described as a calcium supplement except Calciworms.