Worm Harvester Basics

    A Worm Harvester is basically just a Trammel Screen, which is a rotating cylinder with a screen mesh for the sides. There are some Harvesters that work with a vibrating or shaking flat screen, but the most common types are all trammels. As the cylinder rotates, the material inside is rolled across the screen as it moves from the input end to the output end. This forward motion is accomplished by the angle that the harvester is tilted.  As the material is rolling, anything smaller than the holes in the screen will fall through the screen, and the rest will continue till it comes out the output end. At the output end, a cone is installed that can separate most of the worms from the other material that did not go through the screen.

    There are several factors that can affect the efficiency of a Worm Harvester. We will look at each one of these below.

Moisture Level

    If too much material is put in at one time, the screening process will not be efficient, as some of the material will never reach the screen where it could fall through.  The moisture level is important in this, as wet materials tend to stick together and "ball" up from the rolling action. If you take castings that have been screened through an 1/8-inch screen, and soak them in water, very little of it will go back through the same size screen. They will instead form large balls, and roll out of the harvester. This demonstrates the need to have your worm bed as dry as possible before harvesting.

    Worm beds are all wet to some degree. When this moisture level becomes excessive, less slope on the Harvester, and less material put in at one time, can increase the efficiency of the screening process. When the material is dryer, more slope can be used, and more material can be added at one time. The ability of a Worm Harvester to be easily adjusted in slope can be an advantage.

    Most worm farmers will hit their Harvester's screen with a stick from time to time, to knock off particles that are stuck on the screen. Finish nails can be taped to the Jets' rotating hoop where the castors will run over them. This causes the screen to jump, which can dislodge stuck material, just as in hitting it with a stick. With the WW-Jet™Harvesters though, this vibration can be made automatic, and either used or not.


Speed of Rotation

    There is no perfect speed, in RPM's (Revolutions per Minute) for a rotating Worm Harvester. If the Harvester rotates too fast, it will sling worms and material to the side from centrifugal force. If the speed is too slow, it takes much longer for the material to move through the Harvester. As the diameter of the rotating screen increases, the RPM needs to be reduced, to maintain the same speed at the circumference of the barrel. This is the important speed, the inches per minute that the screen moves, not necessarily the RPM that the Harvester moves. WW-Jet™ Harvesters have the proper speed for both diameters.


    The slope of a Worm Harvester will determine how fast the material will move from the input to the output.  A WW-Jet™ Harvester is designed with the most often used slope built in, when the legs are adjusted so that the frame is in a level position. The slope can be easily changed with the adjustable legs, to suit any type of material.

    In general you will increase the slope when the material being screened comes through the screen easily. This will be drier material, material with few worms, and when using a larger size screen mesh.

    The slope is decreased when most of the material is not going through the screen, but rather going out the end. This can happen with wet material, material with many worms, and when using a smaller mesh screen.

    The other factor that works in conjunction with slope is the amount of material put in at any one time. Slowing down on the input quantity is usually needed when decreasing the slope, or the Harvester will overfill and not screen the material completely. When using large mesh screens, and a higher slope, usually more material can be put in at once.

Screen Mesh Size

    WW-Jet™ stocks three size screen meshes: 1/8 inch, 1/4 inch, and 1/2 inch.

1/8 Inch screen mesh is very fine, and your castings will look the best, but you will get the least amount of volume. Most of the worm eggs will not go through this size screen. If the material is very wet, this size screen will do very little without vibration.

1/4 Inch screen mesh is the most commonly used. The castings will still look very good, and you will get more. Some eggs and very small worms can go through. On wet material 1/4 inch mesh screens out much more than 1/8 inch.

1/2 Inch screen mesh is mostly only used when trying to harvest large worms, and as the second or third screen size on a multi-screen Harvester. Many eggs and small to medium worms can go through, and this material would be added back to the bed. Wet material will go through much better than with any smaller size. 

    WW-Jet™ builds Harvesters with one, two, or three different screens. This allows for more different types of screened material at one time. A two screen model, like the 2420 or 3620, can have 1/8" on the top and 1/4"  on the bottom, 1/4" on both, or 1/4" on top and 1/2" on the bottom. A three screen Harvester, like the 2430, is suited for separating large worms, as most everything but the largest worms will have gone through one of the screens before reaching the output. The screens are easily changed with only a screwdriver on a WW-Jet™ Harvester, so you can set it up the way that best suits your beds and needs. You can specify which mesh you prefer installed when ordering, and order additional sizes if desired.

Output Cone and Worm Diverter

    The Output end of a Worm Harvester is generally a cone shape. As the material insides the harvester rolls around, the larger or wetter particles will form into balls, like making a snowball. When these reach the end of the Harvester and get into the cone, the increased slope of the sides of the cone cause them to roll out quickly. The worms tend to stick to the metal of the cone, and do not roll as easy, and therefore will stay in the cone longer. Since the cone is rotating, the longer something stays in it, the further over to the side it will come out. The longer a cone is, with the same slope, the further to the side the worms will go, and the better the separation you will get. The output cone on a WW-Jet™ Harvesters has been designed for optimum worm separation.

    With the WW-Jet™ Diverter shaped like an upside down "V", these two streams are separated enough that you can have the worms land in one container, and everything else in another. The Diverter can be adjusted from side to side, to be able to place it at the right place no matter what the conditions are.

Input Cone on WW-Jet™ Harvesters

    When material is put into any other Worm Harvester, some of it will fall back out. This problem has been addressed with some Harvesters by having the input cylinder be very long. A solid cylinder is doing no screening, and these only make it take longer before the worms can get out. Other put a "ring" around the input cylinder to try to keep material from falling back out. This ring looks very much like the blade on a meat slicer in reverse and can be dangerous for the operator. It also is not entirely effective.

    WW-Jet™ has taken a different and unique approach, by putting a reverse cone on the Input end of all of our Harvesters. The increased slope of this cone pushes the material forward and onto the screens. The decreased time that your worms spend in the Harvester is another plus. Cones are considerably more expensive to build than a cylinder, but WW-Jet™ is able to offer this advancement for less money than its' competitions obsolete designs.

    When you know how they work, and you know how they are built, the WW-Jet™ Worm Harvester stands out as not only the Best designed and built Harvester, but also the Best Value. We came up with our innovations because we use Harvesters, and the other designs just didn't cut it.

For More Information
Please Contact:
Dan Warco
Kazarie Worm Farm
(352) 463-7823